1. If $x+y-2$ is a factor of the polynomial $x^{2}+a x y+b y^{2}-5 x+y+6$ in terms of $x, y$, then the value of $a-b$ is $\qquad$
According to the problem, $(x+y-2)(x+b y-3)=x^{2}+(b+1) x y+b y^{2}-5 x-(2 b+3) y+6$
$$
\Rightarrow\left\{\begin{array}{l}
b+1=a, \\
2 b+3=-1
\end{array} \Rightarrow \left\{\begin{array}{l}
a=-1, \\
b=-2
\end{array} \Rightarrow a-b=1 .\right.\right.
$$