3. Let the midpoint of the chord $AB$ of the circle $x^{2}+y^{2}=9$ be $(1,1)$, and the line $AB$ intersects the $x$-axis at point $P$, then $|PA| \cdot |PB|=$

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Given $M(1,1), k_{A B} \cdot k_{O M}=-1 \Rightarrow k_{A B}=-1 \Rightarrow A B: x+y-2=0$, then $P(2,0)$.
Thus $|P A| \cdot|P B|=(|M A|-|M P|)(|M B|+|M P|)$
$=|M A|^{2}-|M P|^{2}=R^{2}-|O M|^{2}-|M P|^{2}=9-2-2=5$.