答：加號不見了：
4x^2+2xy-2y^2-11x+7y-3=0
看成是關于x的方程
判別式=(2y-11)^2-4*4*(-2y^2+7y-3)
=4y^2-44y+121+32y^2-112y+48
=36y^2-156y+169
=(6y-13)^2
x=[-(2y-11)±√(6y-13)^2]/(2*4)
x1=(2y-1)/4,x2=-y+3
所以：
4x^2+2xy-2y^2-11x+7y-3
=4*[x-(2y-1)/4]*[x-(3-y)]
=(4x-2y+1)(x+y-3)