QPaperGen

\begin{align*}
\text{LHS} &=\frac{\cos(\pi + x)\cos(-x)}{\sin(\pi - x)\cos\left( \frac{\pi}{2} + x \right)}\\&= \frac{(-\cos x)(\cos x)}{(\sin x)(-\sin x)} \\
&= \frac{-\cos^2 x}{-\sin^2 x} \\
&= \frac{\cos^2 x}{\sin^2 x} = \cot^2 x = \text{RHS} \qquad \textbf{Hence proved.}
\end{align*}