Question

How are rigid transformations used to justify the SAS congruence theorem?

Answer 1

Rigid transformations preserve segment lengths and angle measures. If you can find a rigid transformation, or a combination of rigid transformations, to map one triangle onto the other, then the triangles are congruent. To prove SAS, we started with two distinct triangles that had a pair of congruent corresponding sides and a congruent corresponding included angle. Then we performed a translation, followed by a rotation, followed by a reflection, to map one triangle onto the other, proving the SAS congruence theorem.

Answer 2

(Refer to the diagram in the attached photo.)

In this diagram there is defined two Sides and an Angle in between (SAS).

Notice how there are two loose endpoints in the diagram. A single line segment can be drawn connecting the endpoints, forming a unique triangle.

If the original diagram is transformed, the dimensions and angles formed by the third line segment remains the same relative to the first two.

Therefore, if two triangles have the same SAS configuration, then they are congruent.