a.Prove \tan ^{-1} x+\tan ^{-1} y=\tan ^{-1}\left(\frac{x+y}{1-x y}\right) \text { where }-\pi / 2<\tan ^{-1} x+\tan ^{-1} y<\pi / 2 \text { . } \tan ^{-1}(1 / 2)+\tan ^{-1}(1 /

3)=\frac{\pi}{4} Hint: Use an identity for tan(x + y). b. Use part (a) to show that c. Use the first four terms of the Maclaurin series of tan^-x and part (b) to approximate the value of n.