Question

$\sqrt{x-5} . \sqrt{x+5} = (x-5) \geq 0 ; (x+5) \geq 0$

Answer 1

vamos lá...
igualando a zero
$\sqrt{x+5} . \sqrt{x-5} =0 \\ \\ \sqrt{(x+5)(x-5)} =0 \\ \\ \sqrt{x^2-25} =0 \\ \\ eleva~~ ambos~~~membros ~~ao~~quadrado \\ \\ ( \sqrt{x^2-25} )^2=0^2 \\ \\ x^{2} -25=0 \\ \\ x^{2} =25 \\ \\ x=\pm \sqrt{25} \\ \\ x=\pm5$


com
(x-5)≥0     e (x+5)≥0

S={-5,+5}