①4x^2-4x-y^2+4y-3 =4x^2-4x-y^2+4y+1-4 =4x^2-4x+1-y^2+4y-4 =(2x-1)^2-(y^2-4y+4) =(2x-1)^2-(y-2)^2 =(2x-1+y-2)(2x-1-y+2) =(2x+y-3)(2x-y+1) ②待定系数法的经典例子 2x^2-xy-6y^2+7x+7y+3 ＝(x-2y+m)(2x+3y+n...