If cosx + cos2x = 1, the value of sin12x + 3sin8x + sin6x - 1 is:

1 0 sin12x + sin6x 7

0

cosx + cos2x = 1 ⇒ cosx = 1 - cos2x ⇒ cosx = sin2x ∴ sin12x + 3sin10x + 3sin8x + sin6x - 1 = ( sin4x + sin2x)³ - 1 = (cos2x + sin2x) - 1 = 1 - 1 = 0