Question

How do you solve `2cos^2x-5cosx+2=0`?

Answer 1

Call cos x = t

2t^2 - 5t + 2 = (2t - 1)(t - 2)

Solve the 2 basic trig equations:

a. `t = cos x = 1/2 -> x = +- pi/3`

b. t = cos x = 2. Rejected since > 1