Question 645794
Solve the equation 2 cos2 x + cos x − 1 = 0, 0 ≤ x ≤ 2π.
2cos^2x+cosx-1=0
(2cosx-1)(cosx+1)=0
..
2cosx-1=0
cosx=1/2
x=π/3,5π/3
or
cosx+1=0
cosx=-1
x=π