Question

demonstreaza asta $-\sqrt{7} \neq \sqrt{-7}$

Answer 1

Presupunem că $-\sqrt{7}=\sqrt{-7}$

$(-\sqrt{7})^2=(\sqrt{-7})^2$

$7=-7$, fals ⇒ $-\sqrt{7}\neq \sqrt{-7}$