Question

proving theorems
which concept is used to prove that the opposite sides of a parallelogram are congruent?
○ congruent rectangles
○ similar rectangles
○ congruent triangles
○ similar triangles

Explanation:

To prove opposite sides of a parallelogram are congruent, a diagonal of the parallelogram splits it into two triangles. Using properties of parallelograms (alternate interior angles are congruent, shared diagonal is congruent), the two triangles are proven congruent via ASA congruence. Corresponding parts of congruent triangles are congruent, so the opposite sides of the parallelogram are congruent.

Answer:

congruent triangles