Which one of the following angles is not a solution of 2cos^2 θ=1+sin θ

Question

A: 90º B: 180º
C:270º
D:450º
E: none of the above

Answer 1

You could just sub in each of the given choices, or
you could just solve it:

2cos^2 θ = 1+sinθ
2(1 - sin^2 θ) - sinθ - 1 = 0
-2sin^2 θ - sinθ + 1 = 0
2sin^2 θ + sinθ - 1 = 0
(2sinθ - 1)(sinθ + 1) = 0
sinθ = 1/2 or sinθ = -1
θ = 30°, 150°, 270°

so ....