The Square Norm of the Function $f ( x ) = \cos ( 3 x )$

Multiple Choice

The square norm of the function $f ( x ) = \cos ( 3 x )$ on the interval $[ 0 , \pi / 2 ]$ is

A) 1
B) $\pi$
C) $\pi / 2$
D) $\pi / 4$
E) 0