The double-angle formula are sometimes considered a critical part of triginometry. So as result, we are taking a look at the one $\displaystyle \sin\left ( 2A \right )=2\sin\left ( A \right )\cos\left ( A \right )$!

For those who are trying to remember why we rewrote $\displaystyle \sin\left ( 2A \right )$ as $\displaystyle \sin\left ( A+A \right )$, here is why: