x^2-2xy-3y^2=0 （x-y）^2-4y^2=0（x-y）^2=(2y)^2x-y=±2yx-y=2y或 x-y=-2yx1=3y x2=-y将x1,x2分别代入②,得：（3y）^2-y*3y+y^2=3y1=±√21/7（-y)^2-y*(-y)+y^2=3y2=±1∴x1=±3√21/3x2=±1