geometry-quadrilaterals In the following figure, we have two right triangles, ABC and BDC.  Knowing that triangle BDC is isosceles (BD=DC) show that the measure of angle DAC is 45 degrees.
I'm not even sure where to start with this one.  Any help would be greatly appreciated!

Trace the circle whose diameter is the common hypothenuse $BC$. The angles $BAD$ and $DAC$ are both on this circumference and correspond to chords that have equal length ($BD$ and $CD$), so they are equal. Since their sum is $\frac{\pi}{2}$, they both have to be $\frac{\pi}{4}$.
