Answer
3 $|\cos\theta|$
Work Step by Step
Given expression-
$ \sqrt {9 - x^{2}}$
Substituting $3\sin\theta$ for $x$ as given, the expression becomes-
$ \sqrt {9 - (3\sin\theta)^{2}}$
= $ \sqrt {9 -9\sin^{2}\theta}$
= $ \sqrt {9(1 - \sin^{2}\theta)}$
= $ \sqrt {9\cos^{2}\theta}$
{ Writing $(1 - \sin^{2}\theta)$ as $ \cos^{2}\theta$ using first Pythagorean identity}
= 3 $|\cos\theta|$
