Answer
$±\sqrt (1 - \sin^{2}\theta)$
Work Step by Step
Lets begin with Pythagorean identity-
$ \sin^{2}\theta + \cos^{2}\theta$ = 1
Subtracting $\sin^{2}\theta$ from both the sides-
$ \cos^{2}\theta = 1 - \sin^{2}\theta$
taking square root, the equation becomes-
$ \cos\theta = ±\sqrt (1 - \sin^{2}\theta)$
