Mathematics

Problem

Range of

f(x) = \sin^{-1}x + \tan^{-1}x + \sec^{-1}x

is (a)

\left(\frac{\pi}{4}, \frac{3\pi}{4}\right)

(b)

\left[\frac{\pi}{4}, \frac{3\pi}{4}\right]

(c)

\left\{\frac{\pi}{4}, \frac{3\pi}{4}\right\}