X + y = 20
x^2 + y^2 = 218
y = 20 - x
x^2 + (20 - x)^2 = 218
x^2 + 400 - 40x + x^2 = 218
2*(x^2) - 40x + 182 = 0 /2
x^2 - 20x + 91 = 0
D = 400 - 4*1*91 = 400 - 364 = 36
x1 = (20 - 6)/2
x1 = 7
x2 = (20 + 6)/2
x2 = 13
y1 = 20 - 7
y1 = 13
y2 = 20 - 13
y1 = 7
Ответ; х = 7, у = 13 или х = 13, у = 7