Find the Indefinite Integral $$\int \sin ^ { 2 } 3 x d x$$

Multiple Choice

Find the indefinite integral. $$\int \sin ^ { 2 } 3 x d x$$

A) $\frac { 3 x - \sin 3 x \cos 3 x } { 3 } + C$
B) $\frac { 3 x + \sin 3 x \cos 3 x } { 6 } + C$
C) $\frac { 3 x - \sin 3 x \cos 3 x } { 6 } + C$
D) $\frac { 3 x - \sin ^ { 2 } 3 x \cos 3 x } { 6 } + C$
E) $\frac { 3 x + \sin 3 x \cos 3 x } { 3 } + C$