#### Answer

$\sin 2x=2\sin x\cos x$

#### Work Step by Step

Start with the left side:
$\sin 2x$
$=\sin(x+x)$
Use the sum identity for sine on page 673:
$=\sin x\cos x+\cos x\sin x$
$=\sin x\cos x+\sin x\cos x$
$=2\sin x\cos x$
Since this equals the right side, the identity has been proven.