Question:
If in ∆ABC and ∆DEF, ABDE=BCFD, then ∆ABC ∼ ∆DEF when
(a) ∠A = ∠F
(b) ∠A = ∠D
(c) ∠B = ∠D
(d) ∠B = ∠E
Solution:
Given: In $\triangle \mathrm{ABC}$ and $\triangle \mathrm{DEF}, \frac{\mathrm{AB}}{\mathrm{DE}}=\frac{\mathrm{BC}}{\mathrm{FD}}$.
We know that if in two triangles, one pair of corresponding sides are proportional and the included angles are equal, then the two triangles are similar.
Then, $\angle \mathrm{B}=\angle \mathrm{D}$
Hence, $\triangle \mathrm{ABC}$ is similar to $\triangle \mathrm{DEF}$, we should have $\angle \mathrm{B}=\angle \mathrm{D}$.
Hence the correct answer is $(c)$.