2005 AMC 12A Problem 3

A rectangle with a diagonal of length x is twice as long as it is wide. What is the area of the rectangle?

\textbf{(A) } \frac{1}{4}x^2 \qquad \textbf{(B) } \frac{2}{5}x^2 \qquad \textbf{(C) } \frac{1}{2}x^2 \qquad \textbf{(D) } x^2 \qquad \textbf{(E) } \frac{3}{2}x^2

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.