Verify That Each Equation Is an Identity $$\sin ( 4 x ) = ( 4 \sin x \cos x ) \left( 2 \cos ^ { 2 } x - 1 \right)$$

Verify that each equation is an identity.
- $$\sin ( 4 x ) = ( 4 \sin x \cos x ) \left( 2 \cos ^ { 2 } x - 1 \right)$$