Congruency, Enlargement and Combined Transformations
Congruency
Two shapes are congruent when they have exactly the same shape and size.
| English | Congruency |
|---|---|
| Bahasa Melayu | Kekongruenan |
| 中文 | 全等 |
How it is used
Triangle ABC has sides 5 cm, 6 cm, 7 cm and triangle PQR has sides 5 cm, 6 cm, 7 cm, so by the SSS rule the two triangles show congruency and every matching angle is equal.
Where it shows up in SPM
In the Congruency, Enlargement and Combined Transformations chapter (Form 5). In Paper 2 you prove two triangles congruent using SSS, SAS, ASA or RHS, then use the congruency to justify that a side or angle is equal.
Paper 1 tests recognising congruent shapes.
Don't confuse it with
Open the chapter: Congruency, Enlargement and Combined Transformations →
Frequently asked questions
What is enough to prove two triangles are congruent?
Any one of four rules is enough: SSS (three sides), SAS (two sides and the included angle), ASA (two angles and the included side), or RHS (right angle, hypotenuse and one side). Quote the rule you used when you write the proof.
Does AAA prove congruency?
No. Three equal angles only prove the triangles are similar, not congruent, because the shapes can be scaled up or down.
You always need at least one pair of equal sides, so use SSS, SAS, ASA or RHS instead.