Question

(√9 - √7) (√9 + √7)
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Answer 1

$( \sqrt{9} - \sqrt{7} )( \sqrt{9} + \sqrt{7} ) \\ ( \sqrt{9} )^{2} - ( \sqrt{7} )^{2} \\ 9 - 7 \\ 2$

$(a - b)(a + b) = {a}^{2} - {b}^{2}$