question_answer

The value of \[\frac{d}{dx}\left[ \left( \frac{{{\tan }^{2}}2x-{{\tan }^{2}}x}{1-{{\tan }^{2}}2x{{\tan }^{2}}x} \right)\cos 3x \right]\] is

A)  \[\tan 2\,xtan\,x\]          

B)  \[\tan 3\,xtan\,x\]

C)  \[{{\sec }^{2}}x\]       

D)  \[\sec \,x\tan \,x.\]