Rule

Transitive Property of Congruence

If two geometric objects A and B are congruent, and B is also congruent to C, then A and C are congruent.

If A≅ B and B≅ C, then A≅ C.

Proof

This proof can be demonstrated using any geometric figure. For simplicity, the polygons A, B, and C will be considered.

By definition, two figures are congruent if and only if they have the same size and shape. Also, congruent figures can be placed onto each other by a combination of rigid motions. Since A and B are congruent figures, there is a combination of rigid motions that place A onto B.

A maps onto B

In this case, the combination of a rotation and a translation places A onto B. Similarly, since B and C are congruent figures, there is a combination of rigid motions that places B onto C.

B maps onto C

The diagram illustrates with a rotation and a translation, B places onto C. Collectively, the rigid motions that place A onto B and B onto C are a combination of rigid motions. Consequently, this combination of rigid motions places A onto C. Therefore, A and C are congruent figures.

A≅ C

The proof is now complete.

Exercises
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