Use a double-angle formula to rewrite the expression.

Question

1/2 cos^2 x -1/4

Answer 1

Just factor out 1/4:

then use the double angle identity cos(2x) = 2cos²(x) - 1 to get:

Answer 2

1/2 cos^2 x -1/4 = 2cos² x - 1 = 2(1 - sin² x) - 1 = 2 - 2 sin² x - 1

4 4 4

= 1 - 2 sin² x = cos 2x = 1/4 cos 2x

4 4