equations

Express cos 2x in terms of sin x. You will then have a quadratic, which is easily dealt with, as sin x can only range from -1 to +1.

cos 2x = 1 - 2sin^2 x

1-2sin^2 x-sinx=0
1-sinx - 2sin^2 x=0
(1-2sinx)(1+sinx)=0

Equals zero if sinx =1/2 or sinx = -1

Arshad....i think he is asking for general rather than principal values.....:-)