(x+y-2xy)(x+y-2)+(1-xy)^2
=(x+y)^2-2(1+xy)(x+y)+4xy+1-2xy+x^2y^2
=(x+y)^2-2(1+xy)(x+y)+(1+xy)^2
=(x+y)^2-(1+xy)(x+y)-(1+xy)(x+y)+(1+xy)^2
=(x+y)(x+y-1-xy)-(1+xy)(x+y-1-xy)
=(x+y-1-xy)(x+y-1-xy)
=(x+y-1-xy)^2
x^3+2x^2-5x-6
=x^3+3x^2-x^2-5x-6
=x^2(x+3)-(x+2)(x+3)
=(x+3)(x^2-x-2)
=(x+3)(x-2)(x+1)
2x^2-5xy+2y^2+7x-5y+3
=(x-2y+3)(2x-y+1)
設(shè)：
x²+xy+ky²-2x+11y-15
=(x+ay+b)(x+cy+d)
=x^2+cxy+dx+axy+acy^2+ady+bx+bcy+bd
=x^2+(c+a)xy+acy^2+(d+b)x+(ad+bc)y+bd
與上對比,得：
c+a=1
ac=k
d+b=-2
ad+bc=11
bd=-15
解得：
b=-5 d=3或b=3,d=-5
a=(11-b)/(d-b)
a=2,a=-1
a=2時,c=-1 k=-2
a=-1時,c=2 k=-2
因此,k=-2
(6x-9)y=7-4x
y=(7-4x)/(6x-9)
=(1+6-4x)/(6x-9)
=1/(6x-9)-2/3
1/(6x-9)=某整數(shù)n+2/3
1/(6x-9)=n+2/3=(3n+2)/3
1/(2x-3)=3n+2
x=(9n+6+1)/(6n+4)
=3/2+1/(6n+4)
1/(6n+4)=某整數(shù)m+1/2
n=-(4m+3)/(6m+3)=-2/3-1/(6m+3)
要是整數(shù),只能m=0 ,此時,n=-1
1/(6x-9)=2/3-1=-1/3 x=1
y=-1
方程的整數(shù)解為x=1,y=-1