{Х-2У=4 x=4+2y
ХУ+У^2=15 (4+2y)y+y^2=15 3y^2+4y-15=0
y1=[-2-√(4+45)]/3=-3 x1=4-6=-2
y2=[-2+√(4+45)]/3=5/3 x2=4+2·5/3=22/3
проверка
y1=-3 x1=-2
-2-2(-3)=4 верно
(-2)·(-3)+(-3)²=15 верно
y2=5/3 x2=22/3
(22/3)-2·(5/3)=4 верно
(22/3)(5/3)+(5/3)^2=15 верно