待定系数法：设：2x^2-xy-15y^2+6x+4y-4 = (2x+ay+b)(x+cy+d)(2x+ay+b)(x+cy+d)=2x^2+(a+2c)xy+acy^2+(b+2d)x+(ad+bc)y+bd对比系数得到方程组,无解.如果常数项-4改成4就有解2x^2-xy-15y^2+6x+4y-4 = (2x+5y+2)(x-3y+...