Answer
(a) $(-\infty, \infty)$
(b) $[-1,1]$
(c) $\frac{\pi}{2}$
(d) $(-\infty, -1]\cup[1,\infty)$
Work Step by Step
(a) The domain of the cosine function is $(-\infty, \infty)$
(b) The range of the sine function is $[-1,1]$
(c) The least positive value, for which the tangent function is undefined, is $\frac{\pi}{2}$
(d) The range of the secant function is $(-\infty, -1]\cup[1,\infty)$ (assume $y=sec(x)$)
