Practice!

Sample Problem

Simplify 1-2sin2x+sin4x.

Solution

1-2sin2x+sin4x

Let sin2x=u

1-2u+u2=(u-1)(u-1)=(sin2x-1)(sin2x-1)=(-1)(1-sin2x)(-1)(1-sin2x)=(1)(1-sin2x)2=(cos2x)2=cos4x