(Solved): 4. (10 pts) Below is given two circles intersecting at A, and a line tangent to both circles at B a ...

4. (10 pts) Below is given two circles intersecting at $A$, and a line tangent to both circles at $B$ and $C$, respectively. Prove that $\mathrm{m}?BAC=90$. [Hint: This should remind you of an example we did in class. And since you're worried about an angle measure, you might need to angle chase a bit.]