X^2-8x+15=0 X^2+12x+20=0 X^2-5x-6=0 X^2-8x-9=0 Найдите корни уравнения

Решите задачу:

$x^2 - 8x + 15 = 0 \left \{ {{x1+x2 = -p} \atop {x1*x2 = q}} \right. \left \{ {{x1+x2 = 8} \atop {x1*x2 = 15}} \right. \left \{ {{x1 = 5} \atop {x2 = 3}} \right.$

$x^2 + 12x + 20 = 0 D = 64 x1 = - 2 ; x2 = - 10$

$x^2 - 5x - 6 = 0 \left \{ {{x1+x2 = -p} \atop {x1*x2 = q}} \right. \left \{ {{x1+x2 = 5} \atop {x1*x2 = -6}} \right. \left \{ {{x1 = 6} \atop {x2 = -1}} \right.$

$x^2 - 8x - 9 = 0 D = 100 x1 = 9 ; x2 = -1$