Answer
9 (a). $ (x - y) (x + y)$
9 (b). $ (\cos\theta - \sin\theta) (\cos\theta + \sin\theta)$
Work Step by Step
9 (a). Given expression is-
$ x^{2} - y^{2}$
= $ (x - y) (x + y)$
{Recall $a^{2} - b^{2}$ = (a-b)(a+b)}
9 (b).
Given expression is-
$ \cos^{2}\theta - \sin^{2}\theta$
= $ (\cos\theta - \sin\theta) (\cos\theta + \sin\theta)$
{Recall $a^{2} - b^{2}$ = (a-b)(a+b)}
