If $cos^2y+sin\, xy =\lambda, $ then $\frac{dy}{dx}=$

$\frac{cos\, xy}{2\, sin\, y\, cos \, y}$ $\frac{y\, cos\, xy}{xcos xy -2sin ycos y}$ $\frac{ycosxy}{sin2y-xcosxy}$ $-\frac{ycosxy}{sin2y+xcosxy}$

$\frac{ycosxy}{sin2y-xcosxy}$