Geometry(Triangles and Angles): GRE Math Practice Question#21

 
This GRE Math practice problem tests your understanding of angle relationships in a triangle.

In the figure above, $\overline{AB} \perp \overline{BC}$, and $\overline{AB} = \overline{AD}$. What is $y$ in terms of $x$ ?

1. $\quad x-90$
2. $\quad 2x-90$
3. $\quad 90-x$
4. $\quad 90-2x$
5. $\quad \dfrac{x}{2}$