Question

-2x²+2x+40=0 Qual é a resposta certa?

Answer 1

Olá!!!

$- 2 {x}^{2} + 2x + 40 = 0 \: \color{red} { \cdot( - 1) } \\ 2 {x}^{2} - 2x - 40 = 0 \: \color{red} { ( \div 2)} \\ {x}^{2} - x - 20 = 0$

$a = 1 \\ b = - 1 \\ c = - 20 \\ \\ \Delta = {b}^{2} - 4ac \\ \Delta = {( - 1)}^{2} - 4 \times 1 \times ( - 20) \\ \Delta = 1 + 80 \\ \Delta = 81 \\ \\ x = \frac{ - b\pm \sqrt{\Delta} }{2a} \\ \\ x = \frac{ - ( - 1)\pm \sqrt{81} }{2 \times 1} \\ \\ x = \frac{1\pm9}{2} \\ \\ x_{1} = \frac{1 + 9}{2} = \frac{10}{2} = \bf{5} \\ \\ x_{2} = \frac{1 - 9}{2} = - \frac{8}{2} = \bf{ - 4}$

$\boxed{ \bf{S = \{ - 4 , \: 5 \} } }$

Espero ter ajudado! :)