Question

ajuda de novo por favor ^^

Answer 1

$-2x^{2}+7=0\\\\7=2x^{2}\\\\2x^{2}=7\\\\x^{2}=\frac{7}{2}\\\\x=\pm\sqrt{\frac{7}{2}}\\\\\\\boxed{\boxed{S=\{-\sqrt{\frac{7}{2}},\sqrt{\frac{7}{2}}\}}}$

Se preferir com racionalização:

$\boxed{\boxed{S=\{-\frac{\sqrt{14}}{2},\frac{\sqrt{14}}{2}\}}}$
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$x^{2}+1=1\\x^{2}=1-1\\x^{2}=0\\x=\pm\sqrt{0}\\x=\pm0\\x=0\\\\\boxed{\boxed{S=\{0\}}}$
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$\dfrac{5x^{2}}{2}=\dfrac{2}{5}$

Multiplicando em cruz:

$5*5x^{2}=2*2\\\\25x^{2}=4\\\\x^{2}=\frac{4}{25}\\\\x=\pm\sqrt{\frac{4}{25}}\\\\x=\pm\frac{\sqrt{4}}{\sqrt{25}}\\\\x=\pm\frac{2}{5}\\\\\\\boxed{\boxed{S=\{-\frac{2}{5},\frac{2}{5}\}}}$