Answer
$9$
Work Step by Step
RECALL:
(i) $(a+b)(a-b) = a^2-b^2$
(ii) $\sqrt{a}^2=a, a \ge0$
Use rule (i) above to obtain:
$=4^2-\sqrt{7}^2
\\=16-\sqrt{7}^2$
Use rule (ii) above to obtain:
$=16-7
\\=9$
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