​Triangle Congruence Postulates                     Page 2 of 5

Included Sides and Angles

In order to understand some of the ways to prove that triangles are congruent, it's important to understand the meaning of the word "included." Some of these postulates will say that the angle or side must be included - this word basically means in between, or in the middle.

An angle is included (between) the two sides that it touches.  ​

​A side is included between the two angles it touches.

Side-Side-Side Postulate (SSS)

​The SSS postulate says that if all three sides of one triangle are congruent to the three sides of a second triangle, then the triangles are congruent.  Let's say you have one triangle with side lengths of 3, 4, and 7 and a second triangle with side lengths of 3, 4, and 7.  By the SSS Postulate, we know that the triangles must be exactly the same size and shape because it has three sets of congruent sides..

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