Series route: This guide belongs to the complete PSLE Learner’s Guide volume directory. The original PSLE Learning Guide supplies the wider English, Mathematics and Science route, while PSLE Mathematics provide verified subject-specific continuation.
Find your route through this guide
This volume solves one precise learner problem: the learner compares triangle shapes, sloping sides or apparent steepness instead of checking whether the triangles share a base and the same perpendicular height. The aim is not to memorise a slogan. It is to understand the mechanism well enough to recognise the idea when the wording, numbers, diagram or context changes. A Primary 6 learner should be able to explain the decision, perform it under time pressure, and detect a tempting answer that only looks familiar.
- Understand the mechanism before memorising a form.
- Study the worked examples and compare near-misses.
- Repair common misconceptions with targeted tests.
- Complete graded independent practice before reading the answers.
- Use delayed transfer and examination control to make the skill durable.
- Use the parent and tutor notes only after the learner has attempted the work.
The problem beneath the mistake
Place points P and Q anywhere on a line parallel to base AB. Triangles ABP and ABQ can look very different, yet both use base AB and the same perpendicular height.
The area formula is one half times base times perpendicular height. When both factors match, the areas match even if the sloping sides do not.
“Between the same parallels” means the shared base lies on one line and both third vertices lie on another line parallel to it.
A horizontal-looking diagram is not required. The lines may be slanted or vertical; perpendicular distance remains constant between parallel lines.
The third vertices can slide along the upper parallel. This shearing changes side lengths and angles but not base or height.
Equal area does not mean congruent triangles. Perimeters, angles and side lengths can differ while coverage remains equal.
Sharing only a base is insufficient. If the third vertices lie at different perpendicular distances from the base, the areas differ.
Having equal-looking heights is also insufficient unless the base lengths match. Both factors in the formula matter.
A right-angle mark can reveal the perpendicular height, but it may fall outside an obtuse triangle. Distance is measured to the base line, not only the base segment.
The theorem supports quick area transfer. If one same-base triangle has area 36 cm², every triangle with its third vertex on the same parallel line also has area 36 cm².
The reverse needs care. Equal areas on the same base imply equal perpendicular heights, so third vertices may lie on one of two parallel lines, one on each side of the base.
The reliable routine is trace the shared base, locate each third vertex, verify the parallel line or equal perpendicular distance, compare the half-base-height products, then limit the conclusion to area.
Core decision: Triangles with the same base and third vertices on a line parallel to that base have equal area because their base lengths match and the perpendicular distance between the parallel lines is constant.
A useful rule has three parts: a trigger, an operation and a check. The trigger tells you when the rule applies. The operation tells you what to do. The check tells you whether the result still matches the meaning of the question. Learners who remember only the operation often apply it in the wrong place; learners who remember only an example often freeze when the surface details change.
Mechanism: why the rule works
1. Trace the shared base
Both triangles must use the same segment, not merely equal-looking segments.
Diagnostic question: Which exact endpoints belong to both triangles? Reliable response: Highlight the common base.
2. Locate the third vertices
Each remaining vertex determines the triangle’s height above or below the base line.
Diagnostic question: Where does each third vertex lie? Reliable response: Mark the line through them.
3. Verify parallel lines
A line parallel to the base stays at constant perpendicular distance.
Diagnostic question: What proves the lines are parallel? Reliable response: Use arrow marks, a statement or angle reasoning.
4. Use compatible heights
Height is perpendicular to the shared base line, not a sloping side.
Diagnostic question: Where is the right angle? Reliable response: Extend the base line if necessary.
5. Compare area products
The one-half factor, base and height match.
Diagnostic question: Which factors are identical? Reliable response: Conclude equal areas without calculating unknown side lengths.
6. Limit the conclusion
The theorem proves area equality, not congruence or equal perimeter.
Diagnostic question: What remains unproved? Reliable response: Name only the requested quantity.
Worked examples: make the decision visible
Do not race through these examples. Before reading each explanation, name the evidence that matters and the information that does not. Then compare the correct route with the tempting route. That comparison is where the transferable learning sits.
Worked example 1: Direct transfer
Task. Triangles ABP and ABQ share AB, and P and Q lie on a line parallel to AB. Area ABP is 28 cm².
Reasoning. Both triangles have the same base and perpendicular height. The controlling idea is one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. Area ABQ is 28 cm².
Independent check. The equal factors make calculation unnecessary. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 2: Numerical check
Task. AB is 12 cm and the parallel line is 5 cm away.
Reasoning. Both triangle areas are one half × 12 × 5. The controlling idea is one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. Each area is 30 cm².
Independent check. The third-vertex position does not enter the product. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 3: Different slants
Task. P is almost above A while Q is far to the right.
Reasoning. Horizontal offset changes shape but not perpendicular height. The controlling idea is one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. The areas remain equal.
Independent check. Do not use the longer sloping side. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 4: No parallel condition
Task. R lies 4 cm from AB and S lies 7 cm from AB.
Reasoning. The heights differ despite a shared base. The controlling idea is one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. The areas are in ratio 4:7, not equal.
Independent check. Base and one-half factor cancel. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 5: Outside altitude
Task. Q lies beyond B horizontally.
Reasoning. The perpendicular may meet an extension of AB. The controlling idea is one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. The same-base same-height rule still applies.
Independent check. Extend the base line. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 6: Rotated figure
Task. AB is vertical and the third vertices lie on a vertical parallel line.
Reasoning. Perpendicular distance is horizontal but still constant. The controlling idea is one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. The areas are equal.
Independent check. Orientation is irrelevant. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 7: Composite area
Task. A quadrilateral is split into two same-base triangles whose third vertices lie on a parallel.
Reasoning. Each triangular component has equal area. The controlling idea is one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. Use equal halves to compare the composite parts.
Independent check. Check that regions do not overlap unexpectedly. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 8: Reverse reasoning
Task. Two triangles share AB and have equal areas on the same side.
Reasoning. Equal base and equal area force equal perpendicular heights. The controlling idea is one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. Their third vertices lie on a line parallel to AB.
Independent check. State the same-side condition. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Deepening lab: compare cases, conditions and limits
A method becomes independent when you can say where it applies, where it stops and which change would alter the conclusion. The cases below deliberately vary one structural feature at a time. For each case, pause before the analysis and predict whether the core rule remains available. Then name the exact condition that controls the decision. This is harder than repeating a worked solution, but it is also closer to what an unfamiliar examination item demands.
Deepening case 1: Sliding vertex
Case. A third vertex moves along the parallel line.
Analysis. Base and height remain fixed. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Explain area invariance. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 2: Long side
Case. One triangle has a much longer sloping side.
Analysis. Perimeter can change while area stays fixed. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Separate the quantities. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 3: Same base only
Case. Vertices lie on different nonparallel lines.
Analysis. Heights may differ. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Reject automatic equality. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 4: Same height only
Case. Two triangles have equal heights but different bases.
Analysis. Areas follow the base ratio. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Compare products. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 5: Parallel marks
Case. Matching arrow marks show the required lines.
Analysis. Diagram notation supplies the condition. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Cite it explicitly. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 6: Visual parallel
Case. Lines merely look parallel.
Analysis. A not-to-scale drawing is not proof. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Use stated or derived evidence. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 7: Opposite sides
Case. Third vertices lie on parallel lines equally distant on opposite sides of AB.
Analysis. Unsigned areas are equal. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Do not confuse orientation with size. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 8: Two possible loci
Case. All vertices at fixed height from a line form two parallel lines.
Analysis. There is one line on each side. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. State this in reverse reasoning. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 9: Grid model
Case. A grid shows constant row separation.
Analysis. Counting perpendicular intervals verifies height. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Ignore diagonal cell paths. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 10: Coordinate model
Case. Vertices have the same vertical coordinate while AB is horizontal.
Analysis. Equal y-distance gives equal height. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Use coordinates only as evidence. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 11: Altitude outside
Case. The foot falls outside the base segment.
Analysis. Distance to the base line remains valid. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Extend the line. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 12: Congruence trap
Case. Equal areas coexist with different side lengths.
Analysis. Area is one scalar property. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. List what is unproved. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 13: Ratio extension
Case. Heights are in ratio 2:3 on the same base.
Analysis. Areas are in ratio 2:3. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Generalise the theorem. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 14: Base ratio
Case. Bases are in ratio 4:5 at equal height.
Analysis. Areas are in ratio 4:5. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Name the common factor. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 15: Parallelogram link
Case. A diagonal creates equal-area triangles in a parallelogram.
Analysis. The triangles share a base-height relationship through parallel sides. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Connect without replacing the proof. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 16: Median link
Case. A median uses equal bases and a shared height.
Analysis. It is another equal-area mechanism. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Distinguish same base from equal split bases. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 17: Units
Case. Lengths in centimetres produce square centimetres.
Analysis. Final area needs squared units. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Attach the unit. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 18: Scale change
Case. Doubling base and height multiplies each area by four.
Analysis. Equality remains under common scaling. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Check both factors. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 19: Unknown height
Case. Area and shared base can determine height.
Analysis. Height equals twice area divided by base. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Use the compatible pair. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 20: Final audit
Case. Shared base, third vertices, parallel proof, perpendicular distance, formula and conclusion limit complete the method.
Analysis. Each blocks a shortcut. Notice that the answer depends on one shared base and one common perpendicular distance between the parallel lines containing the base and the third vertices; changing a decorative detail would not be enough to change the reasoning.
Challenge. Audit ten figures. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Finish the lab with a blank-page recall. Write the rule, its conditions, one confirming example, one near-miss and one independent check from memory. Compare that page with the article only after finishing. If the rule is correct but the condition is missing, the learning is not yet safe: an overgeneralised rule can produce confident errors. If the condition is correct but no example can be generated, practise construction rather than rereading.
Common misconceptions and targeted repairs
Misconception 1: Same base is enough
What the learner may think. Any two triangles on AB have equal area.
Why it fails. Their third vertices may have different heights. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Check parallel-line or height evidence. Use this short test immediately: Are perpendicular distances equal?
Misconception 2: Same sloping side means same height
What the learner may think. Equal boundary sides control area.
Why it fails. Height must be perpendicular to the base. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Locate the altitude. Use this short test immediately: Is there a right angle?
Misconception 3: Parallel means horizontal
What the learner may think. Only flat lines can be parallel.
Why it fails. Parallelism is a relationship independent of page orientation. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Rotate the reasoning. Use this short test immediately: Do the lines meet if extended?
Misconception 4: Equal area means congruent
What the learner may think. All corresponding sides are equal.
Why it fails. The formula proves only equal coverage. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Limit the conclusion. Use this short test immediately: What congruence data are missing?
Misconception 5: Altitude must be inside
What the learner may think. An outside foot invalidates the height.
Why it fails. Distance to an extended base line is valid. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Extend the base. Use this short test immediately: Is the segment perpendicular?
Misconception 6: Drawing proves condition
What the learner may think. The vertices look level.
Why it fails. Figures may not be to scale. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Cite marks, statements or calculation. Use this short test immediately: What explicit evidence exists?
Graded independent practice
Attempt each item without looking ahead. Write one line that identifies the controlling evidence before writing the final answer. Items 1–3 check recognition, 4–7 require explanation, and the later items change the surface form so that memory alone is insufficient.
Practice 1: Recognition
Question. Two triangles share AB and their third vertices lie on a line parallel to AB. Compare areas.
Explained answer. They are equal.
Why this answer earns trust. Base and perpendicular height match. Transfer variation: State the formula.
Practice 2: Direct
Question. Base 14 cm, height 6 cm. Find each area.
Explained answer. 42 cm².
Why this answer earns trust. One half × 14 × 6 = 42. Transfer variation: Check square units.
Practice 3: Transfer
Question. One area is 37 cm². Find the other under the theorem.
Explained answer. 37 cm².
Why this answer earns trust. Equal factors give equal area. Transfer variation: No side lengths are needed.
Practice 4: Counterexample
Question. Do two triangles sharing only a base have equal area?
Explained answer. Not necessarily.
Why this answer earns trust. Their heights may differ. Transfer variation: Draw two vertices at different distances.
Practice 5: Ratio
Question. Shared base, heights 3:5. Find area ratio.
Explained answer. 3:5.
Why this answer earns trust. Area is proportional to height. Transfer variation: Use sample values.
Practice 6: Orientation
Question. Does a vertical base change the theorem?
Explained answer. No; page orientation does not alter the relationships.
Why this answer earns trust. Perpendicular distance remains the controlling height. Transfer variation: Identify the horizontal altitude.
Practice 7: Limit
Question. Does equal area prove equal perimeter?
Explained answer. No; equal coverage does not fix the boundary length.
Why this answer earns trust. Sloping sides may differ. Transfer variation: Give a sliding-vertex example.
Practice 8: Reverse
Question. Equal areas share AB on the same side. What follows?
Explained answer. Their perpendicular heights are equal, so the third vertices lie on a parallel to AB.
Why this answer earns trust. The common base cancels. Transfer variation: State the same-side qualification.
Practice 9: Rule recall
Question. State the theorem and mechanism.
Explained answer. Same base plus third vertices on a parallel gives equal base-height products.
Why this answer earns trust. Condition and reason are both present. Transfer variation: Recall after one week.
Practice 10: Transfer
Question. Classify twelve diagrams.
Explained answer. Every equality claim cites both shared base and equal height.
Why this answer earns trust. The method transfers. Transfer variation: Include four near-misses.
Delayed transfer: prove that the learning lasts
Transfer test 1: Blank proof
Reconstruct the formula proof after a delay. Do this after a delay, without rereading the worked examples. The purpose is to test retrieval and decision-making, not immediate imitation.
Success criterion. Base, height and one-half factor are explicit. If the criterion is not met, return to the smallest missing decision rather than repeating the entire chapter.
Transfer test 2: Sliding investigation
Move a vertex along a parallel grid line. Do this after a delay, without rereading the worked examples. The purpose is to test retrieval and decision-making, not immediate imitation.
Success criterion. Calculated areas remain equal. If the criterion is not met, return to the smallest missing decision rather than repeating the entire chapter.
Transfer test 3: Reverse locus
Locate possible equal-area third vertices. Do this after a delay, without rereading the worked examples. The purpose is to test retrieval and decision-making, not immediate imitation.
Success criterion. Both parallel lines at fixed distance are identified. If the criterion is not met, return to the smallest missing decision rather than repeating the entire chapter.
Examination control
1. Read the job before the story. Underline the command and the noun it governs. “Explain the change,” “state the word,” “find the fraction” and “identify the evidence” are different jobs even when the surrounding context is similar.
2. Separate given information from remembered information. Use only the facts supplied for the current task plus secure subject knowledge. Do not let a previous question, a familiar worksheet or an expected pattern silently become new evidence.
3. Write enough working to expose the decision. A marker or teacher should be able to see the relationship that justifies the answer. Extra sentences are not automatically stronger; the strongest working is concise, relevant and checkable.
4. Reserve a different-route check. For language, read the sentence for meaning and grammar. For mathematics, estimate or reverse the operation. For science, check the claim against the stated observation and a conservation or fair-test principle.
5. Stop when the requested job is complete. Unrequested speculation can contradict a correct answer. Add detail only when it explains the mechanism or satisfies another explicit part of the question.
Under time pressure, use a compact four-part margin routine: trigger → evidence → operation → check. Trigger names the feature that activates the method. Evidence identifies the exact words, values or observations allowed. Operation performs the language, mathematical or scientific step. Check asks whether the final statement answers the requested job, preserves units or referents, and avoids a stronger claim than the evidence supports.
A compact error log
After practice, do not record only “careless mistake.” Name the broken decision. Useful labels include trigger missed, evidence imported, relationship reversed, referent lost, unit dropped, operation correct but job wrong, and check repeated the same route. Add one prevention cue beside the label. A short accurate log is more useful than a long emotional account because it tells the learner what to do on the next item.
Review the log after two days and again after a week. Reattempt only one or two representative items first. If the method transfers, move to a mixed set. If it fails, repair the exact link between trigger and operation. This spacing matters because a solution can feel obvious while it is still visible and disappear when the page is closed.
Notes for parents and tutors
Use squared paper: keep one base fixed and move the third vertex along a parallel grid line. Calculate several areas before naming the theorem.
Ask for the right angle whenever the learner says height. This prevents sloping sides from entering the area formula.
Compare area and perimeter on two sliding-vertex triangles. Equal area does not mean every measurement stays equal.
The adult’s most useful question is not “Why were you careless?” but “Which decision did the evidence require?” Ask the learner to point to the controlling word, value, relationship or observation. If the learner can explain that link, reduce support. If the learner cannot, model one example and then change the surface details for the next attempt.
Frequently asked questions
What conditions guarantee equal area?
The triangles share a base and have equal perpendicular height, often because their third vertices lie on a parallel line.
Must the triangles look alike?
No; their shapes may differ.
Can the altitude fall outside?
Yes, it may meet an extension of the base.
Does equal area prove congruence?
No; congruence needs additional side or angle evidence.
What if the heights are in ratio 2:3?
The areas are in ratio 2:3 on the same base.
What is the fastest check?
Trace the exact shared base and verify equal perpendicular distance.
Next routes
Return to the complete volume directory to locate the series, use the original PSLE Learning Guide for the foundation route, and continue through PSLE Mathematics for verified subject guidance. The next useful task is a mixed set in which this idea is sometimes relevant and sometimes irrelevant; that is the point at which a learner must choose, not merely copy.