AMC 12 2008b Problem 13

Vertex $E$ of equilateral triangle $\triangle ABE$ is in the interior of unit square $ABCD$. Let $R$ be the region consisting of all points inside $ABCD$ and outside $\triangle ABE$ whose distance from $\overline{AD}$ is between $\frac{1}{3}$ and $\frac{2}{3}$. What is the area of $R$?

(Solution)

\textbf{(A)}\ \frac{12-5\sqrt{3}}{72} \textbf{(B)}\ \frac{12-5\sqrt{3}}{36} \textbf{(C)}\ \frac{\sqrt{3}}{18} \textbf{(D)}\ \frac{3-\sqrt{3}}{9} \textbf{(E)}\ \frac{\sqrt{3}}{12}