Question

prove that a diagonal divides a parallelogram into two congruent triangles ​

Answer 1

consider Δ ABC and Δ ACD

Since the line segments AB+CD are parallel

to each other and AC is a transversal

∠ ACB = ∠ CAD.

AC = AC (common side)

∠CAB = ∠ ACD.

Thus, by ASA criteria

ΔABC ≅ ΔACD

The corresponding part of the congruent

triangle are congruent

AB = CD + AD = BC