1. x-y=7
x=7+y
2. xy= -10
y(7+y)=-10
y^2+7y=-10
y^2+7y+10=0
D=7^2-4*10*1=49-40=9.
y1=(-7+3)/2=-2.
y2=(-7-3)/2=-5,5.
3. x=7+y
x1=7+(-2)=5.
x2=7+(-5,5)=1,5.
6х+у=5