x2+axy+by2-5x+y+6=(x+y-2)*(x+by-3)
=x2+(b+1)xy+by2-5x-(3+2b)y+6
所以有:b+1=a
3+2b=-1
得出a=-1
b=-2
a+b=-3 这是正确答案,望采纳