1)x^2+y^2=74 x-y=22)x^2+4y^2=34x+y=73)x^2-2xy-y^2=1x+y=2

1) x^2+y^2=74X=2+y(2+y)^2+y^2=744+4y+y^2+y^2=742y^2+4y-70=0Y^2+2y-35=0D=4+140=144y1=5y2=-7 => x1=2+5=7; x2=2+(-7)=-52)x^2+4y^2=34x+y=7x=7-y (7-y)^2+4y^2=3449-14y+y^2+4y^2-34=05y^2-14y+15=0D=196-300=-104Корней нет3) x^2-2xy-y^2=1x+y=2y=2-xx^2-2x*(2-x)-(2-x)^2=1x^2-4x+2x^2-4-4x+x^2-1=04x^2-8x-5=0D=64+80=144x1=2,5; x2=-0,5;y=2-x => y1=2-2,5=-0,5; y2=2-(-0,5)=2+0,5=2,5