x-2y=3
3x+2y=1

2x-y=4
3x+7y=1

1)3x+2y=1x=3+2y x=3+2y3(3+2y)+2y=1x=3+2y9+6y+2y=1x=3+2y8y=1-9x=3+2yy=-8/8x=3+2yy=-1y=-1x=3+2×(-1)y=-1x=3-2y=-1x=12)3x+7y=1-y=4-2x3x+7y=1y=-4+2xy=-4+2x3x+7(-4+2x)=1y=-4+2x3x-28+14x=1y=-4+2x-11x=29и тд