x^2 - 16 = 0;
x^2 = 16;
x = +- radicequadrata(16);
x1 = + 4;
x2 = - 4; (due soluzioni).
9x^2 + 13 = 49;
9x^2 = 49 - 13;
9 x^2 = 36;
x^2 = 36 / 9;
x^2 = 4;
x = + - radicequadrata(4);
x1 = + 2;
x2 = - 2.
Ciao @babicella
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$x^2-16 = 0$
$x^2 = 16$
$\sqrt{x^2} = \sqrt{16}$
$x= \pm4$
$9x^2+13=49$
$9x^2 = 49-13$
$9x^2 = 36$
$\dfrac{\cancel9x^2}{\cancel9} = \dfrac{36}{9}$
$x^2=4$
$\sqrt{x^2} = \sqrt4$
$x= \pm2$