Question

$- x^{2} -20x-91=0$

Answer 1

- X^2 - 20X - 91 = 0  /:(-1)
X^2 + 20X + 91 = 0
D = 400 - 364 = 36
X1 = ( - 20 + 6)/2 = - 14/2 = - 7
X2 = ( - 20 -  6)/2 = - 26/2 = - 13

Answer 2

А разве обязательно на -1 делить?

Answer 3

-х²-20х-91=0
х²+20х+91=0
D=400-4*1*91=√36
x1=-20+6/2=-14/2=-7
x2=-20-6/2=-26/2=-13