Congruent shapes
Shapes that are exactly the same size and shape. One can be moved onto the other by sliding, turning or flipping.
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Analogy
Like two identical biscuits cut from the same cutter.
Example
SSS: three sides equalSAS: two sides and the angle betweenASA: two angles and a sideRHS: right angle, hypotenuse, side
In practice
Mass-produced parts, like car doors, must be congruent.
Practice
Flashcards
- Name the four congruence rules for triangles.SSS, SAS, ASA and RHS.
Questions people ask
How can you prove two triangles are congruent?
Show that one of the four rules holds: SSS, SAS, ASA, or RHS for right-angled triangles. You only need one rule, and you must give the reason for each equal part. AAA (three equal angles) is not enough. Write the matching corners in the same order so the equal parts are easy for a marker to follow.
Why is AAA not enough to prove congruence?
Three equal angles only guarantee the same shape, not the same size. A small triangle and a big triangle can have identical angles. Those are similar triangles. For congruence, at least one side length must also match. Think of a small and large photocopy of the same triangle: same angles, different sizes.