x^2+xy-6y^2+x+13y-6
x^2+xy-6y=[x+3y][x-2y]
所以设原式=[x+3y+m][x-2y+n]
=[x+3y][x-2y]+n[x+3y]+m[x-2y]+mn
=[x+3y][x-2y]+[n+m]x+[3n-2m]y+mn
则有：
m+n=1
3n-2m=13
mn=-6
m=-2
n=3
所以原式=[x+3y-2][x-2y+3]