Problem 50E

47-50 Find $y^{\prime}$ and $y^{\prime \prime}$.

47. $y=\cos (\sin 3 \theta)$

48. $y=\frac{1}{(1+\tan x)^{2}}$

49. $y=\sqrt{1-\sec t}$

50. $y=\frac{4 x}{\sqrt{x+1}}$