X=3-y
y²-x=39
x=3-y
y²-(3-y)=39
x=3-y
y²-3+y=39
x=3-y
y²+y-39-3=0
x=3-y
y²+y-42=0
y²+y-42=0
D=1²-4*(-42)*1=1+168=169=13²
y₁=(-1+13)/2=12/2=6
y₂=(-1-13)/2=-14/2= -7
Проверка:
(-7)²-7-42=49-7-42=0
6²+6-42=36+6-42=0
x=3-y
y₁=-7
y₂=6
x₁=3+7
x₂=3-6
y₁=-7
y₂=6
x₁=10
x₂= - 3
y₁= - 7
y₂=6