4) -2x+10y=0
2x-y=9 9y=9 y=1 x=5y x=5 {5;1}
5) x^2+3x-10=0 x1=2 y=3x-10=-4
x2=-5 y=-15-10=-25
6) 9x+3y=18
2x^2-3y=-7
2x^2+9x=11 2x^2+9x-11=0 x=(-9+-13)/4
x1=-5,5 x2=1
y=6-3x y1=6-3(-5,5)=22,5
y2=6-3*1=3
{-5,5;22,5} {1;3}
7) y=x-1
x^2+2x(x-1)-40=0 x^2+2x^2-2x-40=0 3x^2-2x-40=0
x1=4 y1=3
x2=-10/3 y2=-13/3
8) (x-y)(x+y)=8 x+y=-4
(x-y)=-2 x-y=-2 2x=-6 x=-3
2y=-2 y=-1