Question

dentre os numeros -2, 0, 1, 4, quais sao raizes da equação x²-2 x-8=0

Answer 1

$x^{2} -2x-8=0\\\\ a=1;\ b=-2;\ x=-8\\\\ \\ \Delta=b^2-4ac\to \Delta=(-2)^2-4.1.(-8)\to \Delta=4+32\to \Delta=36\\\\ x' \neq x''\\\\\\ x= \frac{-b\pm \sqrt{\Delta} }{2a} \to x= \frac{-(-2)\pm \sqrt{36} }{2.1} \to x= \frac{2\pm 6}{2} \to \\\\\\ x'= \frac{2+ 6}{2} \to x'= \frac{8}{2} \to x'=4\\\\\\ x''= \frac{2- 6}{2} \to x''= \frac{-4}{2} \to x''=-2\\\\\\\\ \boxed{S=\{-2;4\}}$

Answer 2

b2 -4ac
4-4×1.-8
4+32
36

-b+-raiz 36 ÷2a
2+6/2=4

2-6/2=-2

4 e -2