f(x) = tan 2x , f'(x) = ....
using the chain rule : \([\tan(2x)]'=(2x)'\tan'(2x)=\frac{2}{\cos^2(2x)}\)
\(f(x)=\tan 2x\\ f'(x)=\sec^2 2x\cdot2=2\sec^2 2x\)
