If \(\rm y = \sqrt {\sin x + \sqrt {\sin x + \sqrt {\sin x + ... \infty}}}\) then \(\rm \frac {dy}{dx}\) is equal to:
1
\(\rm \frac {\cos x}{2y - 1}\)
2
\(\rm \frac {-\cos x}{2y - 1}\)
3
\(\rm \frac {\sin x}{1 - 2y}\)
4
\(\rm \frac {-\sin x}{1 - 2y}\)