Question

escreva as equações na forma geral e resolva?  
-20=-x-x²

Answer 1

$-20=-x- x^{2} \\ x^{2} +x-20=0\\\\ \Delta=b ^{2}-4ac\\ \Delta=1 ^{2}-4*1*(-20)\\ \Delta=1+80\\ \Delta=81$

$x= \frac{-b\pm \sqrt{\Delta} }{2a}~\to~x= \frac{-1\pm \sqrt{81} }{2*1}~\to~x= \frac{-1\pm9}{2}\begin{cases}x'= \frac{-1+9}{2}~\to~x'=4\\\\ x''= \frac{-1-9}{2}~\to~x''=-5 \end{cases}\\\\\\ \boxed{S=\{-5,4\}}$

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