Question

Question about simplification.

Answer 1

@myininaya

Answer 2

@SithsAndGiggles

Answer 3

\[4-\left(r^2\sin^2\phi\cos^2\theta+r^2\sin^2\phi\sin^2\theta\right)=4-r^2\sin^2\phi\left(\color{red}{\cos^2\theta+\sin^2\theta}\right)=\cdots\]