Question

Multiply $3\sqrt{-7}-5\sqrt{-2}$ by $3\sqrt{-7}+5\sqrt{-2}$

Answer 1

$(3\sqrt{-7}-5\sqrt{-2})\times (3\sqrt{-7}+5\sqrt{-2})$

$=(3\sqrt{7}\text{i}-5\sqrt{2}\text{i})\times (3\sqrt{7}\text{i}+5\sqrt{2}\text{i})$

$=-(3\sqrt{7}-5\sqrt{2})\times (3\sqrt{7}+5\sqrt{2})$

$=-(63+15\sqrt{14}-15\sqrt{14}-50)$

$=-13$