Exercise 2 Page 557

We are asked to determine whether the given triangles are similar.

Notice that $\angle A$ is shared by both triangles. Remember, every angle is congruent to itself.

Also, both $\angle D$ and $\angle B$ have the same measure. This means that $\angle D$ and $\angle B$ are congruent.

As we can see, two angles of one triangle are congruent to two angles of the other triangle. By the rule for Angle-Angle (AA) Similarity, the triangles are similar.