Question

Solve:

2cos^2 theta - 3cos theta+ 1= 0

interval [0, 2ð)

Answer 1

let z = cos theta
then
2 z^2 -3 z + 1 = 0
(2z-1)(z-1) = 0
z = 1/2 or z = 1
cos theta = 1/2 gives theta = 60degrees or pi/3 radians and also -60
cos theta = 1 means 0 or 360