Answer
$a-b^{2}$
Work Step by Step
$(\sqrt a+b)(\sqrt a-b)$
=$\sqrt a(\sqrt a-b)+b(\sqrt a-b)$
=$\sqrt a\sqrt a-b\sqrt a+b\sqrt a-b^{2}$
=$\sqrt a\sqrt a-b^{2}$
=$a-b^{2}$
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