What can you conclude about BC in △ ABC and △ DBC?
See solution.
Practice makes perfect
If we can show that △ ABC ≅ △ DBC , then we know that ∠ A ≅ ∠ D. Since the two triangles share BC as a side, we can by the Reflexive Property of Congruence say that these sides are congruent. Let's mark this in our diagram.
Since the three sides of △ ABC are congruent to corresponding sides of △ DBC, we can by the SSS Congruence Theorem prove that △ ABC ≅ △ DBC. Now we can also say that ∠ A ≅ ∠ D since these are corresponding angles.
