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Secondary 4 Additional Mathematics Tuition: Why Can the Greatest Value Occur at an Endpoint?

Student wearing glasses and a striped tie smiles while holding a Mathematics textbook.

Your child differentiates correctly, finds a turning point, and reports its value as the answer—but the question allows only a restricted interval. Secondary 4 Additional Mathematics tuition should check the domain before accepting that result. The greatest or least permitted value can occur at an endpoint, and an otherwise correct stationary point may lie outside the allowed inputs.

Secondary 4 Additional Mathematics tutorials can make the decision clear: read the permitted interval, find the valid interior stationary candidates, evaluate the original function at those candidates and at included endpoints, then compare the outputs. For the smooth functions on closed intervals used here, that comparison answers a different question from simply naming a local maximum or minimum.

A Secondary 4 Additional Mathematics tutor can preserve your child’s differentiation while repairing the final selection. Parents can bring the original domain, candidate list and first answer. The next useful lesson may be about checking a boundary or distinguishing an input from an output, rather than repeating the derivative rules.

eduKateSG · Secondary 4 Additional Mathematics

Find the question closest to your family

Choose a route, read the explanation, and use only the worked checks that fit your child’s current course.

ROUTE 1 · CHAPTERS 1–2

Read the permitted interval

The permitted interval is part of the question

ROUTE 2 · CHAPTERS 3–5

Build the candidate list

Build the candidate list before comparing outputs

ROUTE 3 · CHAPTERS 6–9

Interpret the comparison

Keep every input tied to its original output

ROUTE 4 · CHAPTERS 10–15

Check and practise independently

An excluded endpoint is not an attained answer

ROUTE 5 · CHAPTERS 16–17

Ask and continue

Questions parents often ask

Full chapter index · Worked learning checks · Additional Mathematics tuition guide

What the first attempt showsTeaching responseFresh independent check
Unrestricted turning point used outside the intervalFilter candidates against the domainA vertex beyond the allowed inputs
No stationary points, so work stopsRead the derivative’s sign and included endpointsA strictly increasing model
Local minimum treated as least overallCompare original outputs at all candidatesA lower endpoint value
Only one tied input is reportedKeep all inputs attaining the winning outputAn endpoint tied with an interior candidate
Excluded endpoint reported as a maximumDistinguish attained output from limiting boundA partly open interval
The permitted domain decides which candidates can answer the question.

CHAPTER 1 OF 17 · Read the permitted interval

1. The permitted interval is part of the question

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A function’s expression tells us how outputs relate to inputs. Its stated domain tells us which inputs the question permits. Both pieces matter when finding the greatest or least value. Do not treat the interval written beside a formula as optional background information.

For f(x)=(x−4)²+1, the unrestricted minimum is 1 at x=4. On 0≤x≤2, however, that input is not allowed. The function decreases throughout the permitted interval, so its least value there is f(2)=5. Its greatest value is f(0)=17.

The algebraic vertex is still correct. The mistake would be presenting it as a result for a different domain. This distinction helps a tutor preserve the student’s good work while teaching the additional decision the actual question requires.

Parents can ask, “Is that input allowed?” A child who checks the original interval before answering has made an important step towards independence. If the learner immediately returns to differentiating, point back to the stated inputs: the missing job may be selection, not calculation.

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CHAPTER 2 OF 17 · Read the permitted interval

2. Local nature and greatest value are different outputs

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A local maximum is higher than nearby values in a suitable neighbourhood. The greatest value on a specified domain is at least as large as every permitted output. A local classification alone does not establish that wider comparison.

Consider f(x)=x³−3x. Its interior stationary points occur at x=−1 and x=1. The first is a local maximum with value 2; the second is a local minimum with value −2. Those local descriptions do not yet tell us the least value on every interval.

On −3≤x≤2, the left endpoint gives f(−3)=−18. That is lower than the local minimum value −2. The least value on this domain is therefore −18 at x=−3. The stationary point’s local nature remains correct; it was simply not the whole answer.

Read whether the task requests stationary coordinates, their nature, a greatest value, a least value or an input that optimises a model. Each wording asks for a particular output. A complete answer to one of these jobs can still be incomplete for another.

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CHAPTER 3 OF 17 · Build the candidate list

3. Build the candidate list before comparing outputs

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For a function continuous on a closed finite interval, greatest and least values are attained. If it is differentiable throughout the interior, an interior extremum must have zero first derivative. Thus the examples here can be checked using the included endpoints and all interior stationary candidates.

That statement has conditions. An undefined expression inside the interval breaks continuity there. A nondifferentiable interior point may also need separate consideration. The selected examples use smooth functions on their stated closed intervals, apart from the explicitly open-interval contrast later on.

Find the derivative and solve f′(x)=0. Filter the resulting inputs against the actual interval. Record the included endpoints separately, then evaluate f at every valid candidate. A small candidate table helps prevent a correct endpoint from being forgotten during a longer calculation.

The candidate list is not a list of derivative values. Substituting each input into f′ only produces gradients, usually zero at the stationary candidates. To compare heights, costs, areas or other outputs, substitute into the original function f.

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CHAPTER 4 OF 17 · Build the candidate list

4. An endpoint can be best without a horizontal tangent

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At an interior differentiable maximum or minimum, neighbouring allowed inputs exist on both sides. An endpoint has a different role: the domain stops there. It can give the greatest or least permitted value even when the derivative of the underlying expression is not zero.

For f(x)=2x+1 on 0≤x≤3, f′(x)=2 everywhere. There are no stationary points. Yet the least value is 1 at x=0 and the greatest is 7 at x=3, because the function increases across the whole permitted interval.

Do not conclude “no maximum” merely because the stationary equation has no solution. The question may be about a closed restricted domain rather than the unrestricted graph. Read the boundaries before deciding that the derivative has supplied no candidates.

A sign argument can sometimes establish the endpoint choice without evaluating many points. A derivative positive throughout the interval shows increase; a derivative negative throughout shows decrease. If the sign changes, inspect the stationary candidates and complete the comparison instead of choosing one endpoint by habit.

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CHAPTER 5 OF 17 · Build the candidate list

5. Classify stationary points only for the job it serves

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A first-derivative sign test or a valid second-derivative test can explain the local nature of a stationary point. That information is useful, but the greatest-value question still requires the comparison over the permitted domain.

For f(x)=x³ on −1≤x≤2, f′(x)=3x² is zero at 0 and positive elsewhere. The graph continues increasing through the horizontal tangent. Its greatest value on this interval is 8 at x=2, and its least value is −1 at x=−1.

When the second derivative is zero at a stationary point, the usual second-derivative test is inconclusive. For x⁴, that happens at 0, yet the function has a minimum there. Another valid argument, such as nonnegativity or the first derivative’s signs, is needed for the local classification.

For the finite candidate comparisons used here, evaluate the stationary candidate regardless of whether its nature has already been classified. If the question separately asks for nature, give the required justification. Keep that local task distinct from selecting the largest or smallest permitted output.

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CHAPTER 6 OF 17 · Interpret the comparison

6. Keep every input tied to its original output

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A greatest value and the input where it occurs are different objects. For f(x)=2x+1 on 0≤x≤3, the greatest value is 7, attained at x=3. Answering only 3 gives the input but not the requested greatest output.

If the question asks for a point, provide both coordinates. If a model asks for a dimension and its associated area, name both quantities with the correct units. Returning to the wording after comparison prevents a technically sound calculation from ending with the wrong object.

Use the original function to evaluate each candidate. If an expression has been rearranged into an equivalent simpler form, that may be a legitimate shortcut, but verify the equivalence and preserve any original domain restrictions.

A parent can ask, “Is that number the input or the result?” The tutor can then see whether the learner’s final interpretation needs work even when differentiation and comparison are accurate. A precise final sentence is part of understanding, not merely presentation.

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CHAPTER 7 OF 17 · Interpret the comparison

7. A greatest value may occur at more than one input

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Do not assume the comparison must select one unique winner. Different permitted inputs can give the same greatest or least value. When the question asks where that value occurs, include all qualifying inputs rather than choosing the first one in the table.

For f(x)=x³−3x on −2≤x≤2, the endpoint values are −2 and 2. The interior stationary outputs are 2 at x=−1 and −2 at x=1. The greatest value 2 occurs at x=−1 and x=2; the least value −2 occurs at x=−2 and x=1.

This example also separates a local description from a global comparison. The endpoint x=2 shares the greatest output with the local maximum at x=−1. There is no contradiction: the two inputs are allowed and produce the same output.

Keep exact values where possible so a true tie is not obscured by different rounding. If several candidates appear numerically close, compare their exact expressions or use adequate precision before concluding that one is larger.

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CHAPTER 8 OF 17 · Interpret the comparison

8. Check the formula’s domain as well as the stated interval

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Some expressions require a positive input or a nonzero denominator. For ln x, x must be positive. For x+1/x, x cannot be zero. An interval must be read together with these restrictions, not treated as permission to evaluate an undefined input.

On 1≤x≤e², ln x is continuous and strictly increasing because its derivative is 1/x>0. The least value is 0 at x=1 and the greatest is 2 at x=e². There is no interior stationary point to find.

For x+1/x on 1/2≤x≤3, the function is well defined throughout. The derivative 1−1/x² gives an interior stationary candidate x=1. Comparing the outputs 5/2, 2 and 10/3 gives least value 2 at 1 and greatest value 10/3 at 3.

Do not extend the same closed-interval argument across x=0 for that reciprocal expression. If an unfamiliar question includes a singularity or another break, bring the exact domain to the teacher or tutor. The comparison method’s assumptions need to be checked before it is used.

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CHAPTER 9 OF 17 · Interpret the comparison

9. A model restriction can rule out the familiar optimum

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A mathematical model may restrict an input for geometric, practical or stated task reasons. The unconstrained optimum remains a useful reference, but it is not automatically an available choice. Apply the model’s actual restriction before interpreting the result.

Suppose a supplied rectangular-area model is A(x)=x(12−x), with 2≤x≤5. Its unrestricted maximum occurs at x=6, but that input is excluded. On the stated interval A′(x)=12−2x is positive, so the greatest permitted area is A(5)=35 square units.

The least permitted area is A(2)=20 square units. The other side lengths are 12−x, so the endpoint choices still give positive dimensions. These are results for the supplied model and domain; they do not claim that a real design has no additional constraints.

If inputs must be whole numbers rather than a continuous interval, compare the permitted discrete choices using the model. Continuous differentiation can help locate promising choices, but it does not make a fractional input available. The wording decides which kind of selection is appropriate.

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CHAPTER 10 OF 17 · Check and practise independently

10. An excluded endpoint is not an attained answer

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A closed interval includes both endpoints; an open or partly open interval may not. The existence guarantee for continuous functions on closed finite intervals should not be transferred automatically to an interval with a missing boundary.

For f(x)=x² on 0≤x<2, the least value is 0 at x=0. The outputs approach 4 as x approaches 2 from below, but x=2 is excluded. Every permitted output is less than 4, so there is no greatest attained value on this domain.

Calling 4 the greatest value would confuse a limiting upper bound with an output reached by an allowed input. For any x<2 in this interval, a slightly larger allowed x gives a larger square. That explains why no single input supplies the greatest output.

Use this contrast at the learner’s appropriate taught stage. It is not a reason to make every routine closed-interval question complicated. Its practical lesson is to read inclusive and exclusive endpoints accurately and explain why a proposed optimum is or is not attained.

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CHAPTER 11 OF 17 · Check and practise independently

11. Let the comparison decision guide the tuition lesson

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Bring the original function, domain, derivative, stationary candidates, endpoint evaluations and final interpretation. Include the first attempt before corrections, the current school topic sequence and teacher feedback. The tutor can identify whether the gap is differentiation, domain reading, comparison or answering the requested quantity.

If the stationary point lies outside the interval, practise filtering candidates. If there are no stationary points and the learner stops, use an increasing function on a closed interval. If the chosen local minimum is not the least permitted value, compare it with a boundary. If one tied input is missed, ask where the winning output is attained.

SEAB’s 2027 SEC G3 Additional Mathematics syllabus includes increasing and decreasing functions, stationary points, the second-derivative test and applications to maxima and minima. The checks here are selected learning examples, not full syllabus coverage or paper predictions. Confirm the student’s actual subject level and examination year with the school and consult the official sources below.

eduKateSG small-group tutorials use up to three students. Confirm current suitability, availability, fees, duration, location and attendance arrangements directly. Parents do not need to differentiate every model: asking which inputs are permitted, whether both endpoints were considered and what the final number represents gives the tutor a focused starting point.

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CHAPTER 12 OF 17 · Check and practise independently

12. A lesson that changes the interval rather than the derivative

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Imagine a learner given the supplied model Q(t)=−t²+8t+3 on 0≤t≤2. The student differentiates correctly, obtains Q′(t)=−2t+8, finds t=4 and reports the maximum value 19. The calculation describes the unrestricted quadratic, but t=4 is outside the given domain.

The tutor preserves the derivative and asks the learner to mark the allowed interval. There is no interior stationary candidate in 0≤t≤2. The included endpoints give Q(0)=3 and Q(2)=15. Since the derivative is positive throughout this interval, Q increases and its greatest permitted value is 15 at t=2.

Next change only the domain to 0≤t≤6. The same stationary input t=4 is now allowed. The candidate outputs are 3 at 0, 19 at 4 and 15 at 6. The greatest value becomes 19 at t=4. The expression and differentiation have not changed; the permitted inputs have.

A further question asks for the least value on 0≤t≤6. The answer is 3 at t=0, not the stationary output. This tests whether the learner reads the requested comparison rather than assuming that every optimisation task ends at the derivative’s zero.

The tutor then asks the child to state both the output and the input clearly. Q(t) here is an illustrative mathematical quantity, not a measured real process. Any physical meaning, units or additional restrictions would have to come from the actual problem.

Parents can ask which decision is now independent: checking the interval, building the candidate list, comparing outputs or naming the final quantity. A later fresh function can test that decision without supplying a cue. The example does not promise a score gain; it shows how to turn correct differentiation into a complete domain-aware answer.

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CHAPTER 13 OF 17 · Check and practise independently

13. Worked comparisons: endpoints and stationary candidates

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1. A vertex outside the permitted inputs

Try first. Find greatest and least values of (x−4)²+1 on 0≤x≤2.

Worked reasoning. The derivative is 2(x−4), negative on this interval. The stationary input 4 is excluded. Endpoint outputs are 17 at 0 and 5 at 2, so greatest value is 17 at 0 and least is 5 at 2.

Check. Squared distance from 4 decreases across the permitted interval.

Error to notice. The unrestricted minimum 1 is not reached here.

Independent variant and answer. On 1≤x≤3, the same function has greatest value 10 at 1 and least value 2 at 3.

What this tells the tutor. Check whether the learner applies the interval before reporting the vertex.

The first task isolates the domain decision with an uncomplicated quadratic. If the learner reports 1, ask which permitted input achieves it. That question preserves the correct vertex calculation while revealing why it is not an answer to the restricted problem.

2. No stationary points does not mean no extrema

Try first. Find greatest and least values of 2x+1 on 0≤x≤3.

Worked reasoning. The derivative is 2>0, so the function increases. The least value is 1 at x=0, and the greatest is 7 at x=3. Neither endpoint needs zero gradient to be optimal on the interval.

Check. Endpoint substitution gives the same order as the derivative sign.

Error to notice. Do not stop after observing that 2=0 has no solution.

Independent variant and answer. For 5−3x on 0≤x≤2, greatest value is 5 at 0 and least value is −1 at 2.

What this tells the tutor. Ask how the derivative sign selects the relevant boundary.

An increasing line is a helpful contrast because the stationary equation cannot produce a candidate. The learner has to return to the domain and the meaning of increase. Once that reasoning is clear, a more complicated increasing function can test the same decision without changing the principle.

3. An interior candidate ties with an endpoint

Try first. Find greatest and least values of x³−3x on −2≤x≤2, including where they occur.

Worked reasoning. The derivative 3(x²−1) gives interior candidates −1 and 1. Endpoint and candidate outputs are −2, 2, −2 and 2 at inputs −2, −1, 1 and 2 respectively. Greatest value 2 occurs at −1 and 2; least value −2 occurs at −2 and 1.

Check. All four inputs are allowed, so the ties must be retained.

Error to notice. A correct value can still have an incomplete attainment list.

Independent variant and answer. On −1≤x≤1, greatest value is 2 at −1 and least value is −2 at 1.

What this tells the tutor. Check whether the final answer reports every winning input.

A tied value deserves a complete final sentence. Encourage the student to keep input-output pairs together during comparison rather than writing an unordered list of numbers. This makes it easier to see which two inputs attain the same greatest or least output.

4. A lower endpoint defeats a local minimum

Try first. Find greatest and least values of x³−3x on −3≤x≤2.

Worked reasoning. The interior candidates remain −1 and 1, with outputs 2 and −2. Endpoints give −18 and 2. Thus least value is −18 at −3; greatest value 2 is attained at −1 and 2.

Check. Changing the domain changed the least value without changing the derivative.

Error to notice. The local minimum at 1 is not the least value on this interval.

Independent variant and answer. On −2≤x≤3, greatest value is 18 at 3; least value −2 occurs at −2 and 1.

What this tells the tutor. This checks a global comparison rather than local classification alone.

Changing only one endpoint keeps the derivative familiar while testing the new comparison. If the student repeats the previous least value, the issue is likely the domain check rather than differentiation. Ask for the updated endpoint output before revisiting any derivative rule.

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CHAPTER 14 OF 17 · Check and practise independently

14. Worked comparisons: logarithms, flat points and domains

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5. An increasing exponential

Try first. Find greatest and least values of e^x on 0≤x≤ln 3.

Worked reasoning. Its derivative e^x is positive, so there are no interior stationary candidates. Included endpoint outputs are 1 and 3. Least value is 1 at 0; greatest value is 3 at ln 3.

Check. The derivative’s positivity covers the entire allowed interval.

Error to notice. A stationary equation is not the only route to an endpoint optimum.

Independent variant and answer. On −ln 2≤x≤ln 2, least value is 1/2 at −ln 2 and greatest is 2 at ln 2.

What this tells the tutor. Ask why the monotonic conclusion is justified across the interval.

For this exponential, the positivity of the derivative is a general sign argument, not a conclusion from one sample point. The tutor can ask why the sign holds everywhere in the interval. That explanation justifies selecting the endpoints without inventing a turning point.

6. A logarithm on a valid domain

Try first. Find greatest and least values of ln x on 1≤x≤e².

Worked reasoning. All inputs are positive, and the derivative 1/x is positive throughout. Least value is ln 1=0 at 1; greatest value is ln(e²)=2 at e².

Check. The function is continuous on this closed interval.

Error to notice. Do not apply ln x to zero or negative inputs.

Independent variant and answer. On 1/e≤x≤e, least value is −1 at 1/e and greatest value is 1 at e.

What this tells the tutor. Check the formula’s own domain before using the interval method.

A domain condition and a stated interval need to agree. This logarithm example is well defined throughout the permitted interval, so endpoint selection follows cleanly. If a different task approaches an excluded or undefined input, the learner must inspect that new condition rather than copying the same existence conclusion.

7. A stationary point without a turn

Try first. Find greatest and least values of x³ on −1≤x≤2.

Worked reasoning. The derivative 3x² gives stationary candidate 0. Compare f(−1)=−1, f(0)=0 and f(2)=8. Least value is −1 at −1; greatest is 8 at 2. The stationary point is not a local extremum.

Check. The cube function increases through the horizontal tangent.

Error to notice. Zero derivative identifies a candidate, not an automatic greatest output.

Independent variant and answer. On −2≤x≤1, least value is −8 at −2 and greatest is 1 at 1.

What this tells the tutor. Ask what the comparison adds beyond finding the derivative’s zero.

The cube example separates a stationary candidate from a turning point. It is still included in the comparison, but it does not supply either extremum on the given interval. Ask the child what was learned from the derivative and what was learned from evaluating the candidates.

8. Zero second derivative at a true minimum

Try first. Find greatest and least values of x⁴ on −1≤x≤2.

Worked reasoning. The first derivative 4x³ gives candidate 0. Although the second derivative 12x² is zero there, x⁴ is nonnegative and reaches 0 at 0. Endpoints give 1 and 16. Least value is 0 at 0; greatest is 16 at 2.

Check. The first derivative changes from negative to positive at 0.

Error to notice. Second derivative zero does not force a point of inflexion.

Independent variant and answer. On −2≤x≤1, greatest value is 16 at −2 and least is 0 at 0.

What this tells the tutor. Use a valid local argument while keeping the endpoint comparison separate.

The quartic is a useful contrast because its flat point really is a minimum, even though the usual second-derivative test gives no decision. A nonnegativity argument or first-derivative sign test explains that nature. The greatest-value result still comes from considering the permitted endpoint.

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CHAPTER 15 OF 17 · Check and practise independently

15. Worked comparisons: models, open bounds and restrictions

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9. A reciprocal needs a valid interval

Try first. Find greatest and least values of x+1/x on 1/2≤x≤3.

Worked reasoning. The derivative is 1−1/x². The only interior stationary input is 1. Compare outputs 5/2 at 1/2, 2 at 1 and 10/3 at 3. Least value is 2 at 1; greatest is 10/3 at 3.

Check. The entire interval avoids the undefined input 0.

Error to notice. The negative stationary input −1 is outside this domain.

Independent variant and answer. On 1/4≤x≤2, greatest value is 17/4 at 1/4 and least is 2 at 1.

What this tells the tutor. Check both stationary filtering and the denominator restriction.

The reciprocal task has a stationary solution outside the interval as well as a denominator restriction. Keep those two checks distinct. One removes an otherwise meaningful but disallowed input; the other prevents evaluating the expression where it is undefined.

10. A product model with an interior maximum

Try first. Find greatest and least values of x²e^(−x) on 0≤x≤3.

Worked reasoning. The derivative is e^(−x)x(2−x). Its interior stationary input is 2; x=0 is already an endpoint. The function increases to 2 and decreases afterwards. Greatest value is 4/e² at 2. All outputs are nonnegative, and least value is 0 at 0.

Check. The endpoint at 3 has value 9/e³, below the interior maximum.

Error to notice. Do not discard the original endpoint merely because it is also a derivative zero.

Independent variant and answer. On 0≤x≤1, the function increases; least value is 0 at 0 and greatest is 1/e at 1.

What this tells the tutor. The same derivative can lead to an endpoint or interior optimum when the interval changes.

A product-rule derivative adds algebra without changing the candidate method. The endpoint at zero and the interior stationary input should be recorded once each. The shorter-interval variant tests whether the learner can apply the same derivative information to a different permitted set.

11. A trigonometric restricted interval

Try first. Find greatest and least values of sin x on 0≤x≤5π/6, with x in radians.

Worked reasoning. The derivative cos x vanishes at the interior input π/2. Candidate outputs are 0 at 0, 1 at π/2 and 1/2 at 5π/6. Greatest value is 1 at π/2; least is 0 at 0.

Check. The derivative changes from positive to negative at π/2.

Error to notice. Use the stated radian interval rather than degree inputs copied from another task.

Independent variant and answer. On π/6≤x≤π/3, greatest value is √3/2 at π/3 and least is 1/2 at π/6.

What this tells the tutor. Check which derivative zeros actually lie inside the given bounds.

The sine example combines derivative-zero selection with a stated angle interval. The learner should identify π/2 as an interior candidate in the main task but not in the smaller variant. Exact endpoint outputs make the comparison clearer than prematurely rounded calculator values.

12. An excluded endpoint prevents attainment

Try first. Does x² have a greatest value on 0≤x<2?

Worked reasoning. No. It increases across this interval and approaches 4 as x approaches 2, but 2 is excluded. Every permitted output is below 4. Its least value is 0 at the included input 0.

Check. For any permitted x<2, a larger permitted input gives a larger square.

Error to notice. A limiting upper bound is not an attained greatest value.

Independent variant and answer. On 0<x≤2, greatest value is 4 at 2, but there is no attained least value; outputs approach 0.

What this tells the tutor. Ask whether the proposed input is included before naming an optimum.

Use the partly open interval to test whether the learner distinguishes an included boundary from an approached one. The conclusion of no attained optimum needs a reason, not just a crossed-out endpoint. A slightly larger or smaller permitted input supplies that explanation in this simple model.

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CHAPTER 16 OF 17 · Ask and continue

16. Questions parents often ask

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Must the derivative be zero at the greatest value?

Not if the greatest permitted value occurs at a boundary. An interior differentiable extremum has a different condition from an endpoint optimum.

Is a local maximum always the greatest value?

No. Local nature describes nearby behaviour. The greatest value on a specified domain requires a comparison over the permitted inputs.

What if there are no stationary points?

Check the interval and the derivative’s sign. A continuous increasing or decreasing function on a closed interval can attain its extrema at the endpoints.

Do we substitute into the derivative to compare candidates?

No. Substitute the candidate inputs into the original function to compare outputs. The derivative describes gradients.

Can two inputs give the same greatest value?

Yes. Report the value and all qualifying inputs if the question asks where it is attained.

Does second derivative zero prove inflexion?

No. The usual second-derivative test is inconclusive there. Use another valid argument when local nature is requested.

Can an excluded endpoint still give the answer?

It cannot be an attained optimum unless its output is also reached at an allowed input. A limiting value and a greatest or least attained value are different claims.

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CHAPTER 17 OF 17 · Ask and continue

17. Continue with the closest reading route

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For the separate question of local classification, read the stationary points and points of inflexion guide. Then return to the permitted-domain comparison when the task asks for a greatest or least value.

For the level-specific programme route, read the Secondary 4 Additional Mathematics guide. For wider programme context, use the eduKateSG Additional Mathematics tuition guide. For examination details, consult SEAB’s 2026 O-Level syllabus listing, 2027 SEC G3 syllabus listing and 2027 SEC G2 syllabus listing. Check the actual subject level and examination year with the school.

eduKateSG small-group tutorials use up to three students. For current suitability and arrangements, visit the Class Enquiries page.

To enquire about current class suitability and practical arrangements, contact eduKateSG about Secondary 4 Additional Mathematics. Bring recent work and a realistic timetable so the first discussion can identify a useful next step.

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