$f(x)=\cos x ; P=\sin ^{-1} \frac{2}{\sqrt{5}}-\frac{1}{2} \sin ^{-1} \frac{3}{5}+\sin ^{-1} \frac{1}{\sqrt{10}}$

(i)

(ii) $\sin (\pi \sin x)+\cos (\pi \cos x)=0$

(i)

(ii) $g(x)=\frac{2 \tan \frac{x}{2}}{1+\tan ^{2} \frac{x}{2}}, f(x)=\frac{1-\cos ^{2} \frac{x}{2}}{1+\cos ^{2} \frac{x}{2}}$