Solve the equation : 2*sin^2 x + cos x - 1 = 0

The equation
`2*sin^2 x + cos x - 1 = 0` has to
be solved for x.

This trigonometric
equation has both sin
x as well as cos x. It is possible to write `sin^2x = 1 - cos^2x` . This

eliminates sin x and would allow the equation to be written as a quadratic in terms of
cos
x.