I am trying to differentiate with respect to $x$, $y = \cos^2{x}$
Using the chain rule and my working out is this:
\begin{align*}\frac{dy}{dx} &= 2 \cos(x)(-\sin(x)) \\ &= -2 \sin x \end{align*} I am not sure how to get to the correct answer of $-\sin{(2x)}$.
Should I be using the chain rule or maybe the product rule?
Please help, Thanks in advance