1).x=1-2y
(1-2y)*y=-1
x=1-2y
y-2y^2=-1
x=1-2y
-2y^2+2y+1=0
Д = 1+4×2×1=9
Y1=1/2=0.5
Y2=1
X1=1-2*0.5=0
X2=1-2*-1=3
2).x^2+x*(-4+x)=6
y=-4+x
x^2-4x-6=0
Д=16+8*6=64
X1=-1
X2=3
Y1=-4-1=-5
Y2=-4+3
3).4x^2-xy=26
3x^2+xy=2
4x^2-2+3x^2-26=0
xy=2-3x^2
7x^2=28
x^2=4
x=2
xy=2-3*4=-10
y=-10-2=-12