Question

Quais são as raizes de -7x²+28=00?

Answer 1

-7x² + 28 = 0 

-7x² = -28 

x² = -28/-7

x² = 4

x = ±√4

x = ±2

S = {-2,2}

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15/02/2016
Sepauto - SSRC
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Answer 2

$-7x^2+28=0\to \\\\ -7x^2=-28~.(-1)\to\\\\ 7x^2=28\to\\\\ x^2 = \dfrac{28}{7}\to\\ \\x^2=4\to\\ x=\pm \sqrt{4}\to\\\\ \underline{~x=\pm 2~}\\\\\\ \large\boxed{S=\{-2~;~2\}}$