Which one of the following angles is not a solution of 2cos^2q = 1+sinq ?

Question

(A) 90° (B) 180° (C)270° (D) 450° (E) none of the above.

Answer 1

2cos^2 x = 1+sinx
2(1 - sin^2 x) = 1 + sinx
2 - 2sin^2 x = 1 + sinx
2sin^2 x + x -1 = 0
(2sinx - 1)(sinx + 1) = 0
sinx = 1/2, so x = 30°, 150°
or
sinx = -1, so x = 270°

so which of those things is not like the other?