Find the Derivative Of $f(x)=\sin 5 x \cos 4 x$
A)

Multiple Choice

Find the derivative of $f(x) =\sin 5 x \cos 4 x$ .

A) $f^{\prime}(x) =-5 \cos 5 x \cos 4 x+4 \sin 5 x \sin 4 x$
B) $f^{\prime}(x) =20 \cos 5 x \sin 4 x$
C) $f^{\prime}(x) =-20 \cos 5 x \sin 4 x$
D) $f^{\prime}(x) =5 \cos 5 x \cos 4 x-4 \sin 5 x \sin 4 x$