Question

como faço isso X²+ X - 20 = 0

Answer 1

$a {x}^{2} + bx + c = 0 \\ {x}^{2} + x - 20 = 0 \\ a = 1 \\ b = 1 \\ c = - 20 \\ x = \frac{ - b + - \sqrt{ {b}^{2} - 4 \times a \times c} }{2 \times a} \\ x = \frac{ - ( + 1) + - \sqrt{ {1}^{2} - 4 \times 1 \times ( - 20) } }{2 \times 1} \\ x = \frac{ - 1 + - \sqrt{81} }{2} \\ x = \frac{ - 1 + - 9}{2} \\ x 1= \frac{ - 1 + 9}{2} = \frac{8}{2} = 4 \\ x2 = \frac{ - 1 - 9}{2} = \frac{ - 10}{2} = - 5$