Question 20
Two circles with centers $O_1,O_2$ are externally tangent at $M$. The lines $AB$ and $CD$ are common external tangents, with contact points as shown. Given $O_2E\perp O_1A$, $\angle AO_1C=120^\circ$ and $O_2B=1$ cm, find the shaded area between the two circles and the tangent segment $AB$. Leave your answer in terms of $\pi$.
