91Ó°ÊÓ

Find the critical points of the function \(f(x)=x+\cos ^{-1} x+1\).

Let \(f(x)=\sin ^{2} x-(2 a+1) \sin x+(a-c) .\) If \(f(x) \leq 0\) for all \(x\) in \(\left[0, \frac{\pi}{2}\right]\), then the range of \(a\) is (a) \([-3,0]\) (b) \([3, \infty)\) (c) \([-3,3]\) (d) \((-\infty, 3]\).