Question

решите системное уровнение
{X^2-y=21
{X+y=9

Answer 1

Сложим
x^2 + x = 30
x^2 + x - 30 = 0 
D = 1 + 4*30 = 121
x1 = ( - 1  + 11)/2 = 5
x2 = ( - 1 -  11)/2 = - 6

x1 = 5
y1 = 9 - x1 = 9 - 5 = 4

x2 = - 6
y2 = 9 - x1 = 9 + 6 = 15

Ответ
( 5; 4) ; ( - 6; 15)