Question 1140882
If this is 2 cos^3 theta+2 cos^2 theta-cos theta-1=0
(which makes sense, because otherwise you could combine the second and third terms)
then it factors into (2cos^2 theta-1) (cos theta+1)=0
and theta =+/- sqrt(2)/2 (45, 135 225, 315 deg)
and -1 (180 degrees)