Question #b6403

1 Answer
Jun 19, 2017

x~=126.38° or x~=32.53°

Explanation:

Since cos2x=cos^2x-sin^2x, you get:

cosx=2cos^2x-2sin^2x

Then, since sin^2x=1-cos^2x, you get:

cosx=2cos^2x-2+2cos^2x

and you would solve the equation:

4cos^2x-cosx-2=0

by using the quadratic formula, then

cosx=(1+-sqrt33)/8

Then x=cos^-1((1+-sqrt33)/8)

x~=126.38° or x~=32.53°