Brainlag PlusThe four conditions that prove two triangles are congruent, the two that do not, and how to write a short proof.
Same shape, same size
Two shapes are congruent if one fits exactly on top of the other, perhaps after turning or flipping it.
Translations, reflections and rotations always give congruent images. Two triangles are congruent if they share any one of these sets of facts:
- SSS: all three sides are equal.
- SAS: two sides and the angle between them are equal.
- ASA: two angles and the side between them are equal. (Because the third angle then matches too, any side in the same position will do; some books call that AAS.)
- RHS: both have a right angle, equal hypotenuses and one other equal side.
The rest of this lesson and its 8 practice questions are in Plus.
Screen 1 of 4, free to read.
- 8 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards