MathNet 2014 Question 75

In $\triangle ABC$, $\angle A = 80^\circ$, $\angle B = 30^\circ$, and $\angle C = 70^\circ$. Let $BH$ be an altitude of the triangle. Extend $BH$ to a point $D$ on the other side of $AC$ so that $BD = BC$. Find $\angle BDA$.