X²-2xy+y²=25 (x-y)²=25 x-y=5 x-y=-5
2x²-2xy-y²=11 2x(x-y)-y²=11 2x*5-y²=11 2x*(-5)-y²=11
x-y=5 x=5+y: x-y=-5 x=y-5
10(5+y)-y²=11 -10(y-5)-y²=11
50+10y-y²=11 -10y+50-y²=11
-y²+10y+50-11=0 -y²-10y+50-11=0
-y²+10y+39=0 -y²-10y+39=0
D=10²-4*(-1)*39=100+156=256 D=(-10)²-4*(-1)*39=100+156=256
y₁=(-10-16)/-2=13 x₁=5+13=18 y₁=(10-16)/-2=3 x₁=3-5=-2
y₂=(-10+16)/-2=-3 x₂=5+(-3)=2 y₂=(10+16)/-2=-13 x₂=-13-5=-18