A triangular park is enclosed on two sides by a fence and on the third side by a straight river bank. The two sides having fence are of same length $x$. The maximum area enclosed by the park is :

Question

( A ) $\pi x^2$
( B ) $\frac{1}{2} x^2$
( C ) $\sqrt{\frac{x^3}{8} }$
( D ) $\frac{3}{2} x^2$