Xy-x=4 2x+y=7 --------------------- y=7-2x x(7-2x)-x=4 --------------------- y=7-2x -2x^2+6x=4 --------------------- y=7-2x x^2-3x+2=0 --------------------- y=7-2x (x-2)(x-1)=0 --------------------- x=2 x=1 y=5 y=3