1. In Rt $\triangle ABC$, $\angle C=90^{\circ}$, $O$ is the incenter, $OE \perp BC$ at $E$, $OF \perp AC$ at $F$. Extend $AC$ to $P$, extend $BC$ to $Q$, such that $AP=BQ=AB$. Try to compare the area of $\triangle CPQ$ with the area of quadrilateral $OECF$.
(提示: Let $B C=a, C A=b, A B=c$. Then
$$
\begin{array}{l}
S_{\triangle C P Q}=\frac{1}{2}(c-a)(c-b) \\
=\frac{1}{2} a b-\frac{1}{2} c(a+b-c) .
\end{array}
$$

Using the equivalent relationship to substitute $a b$ in the formula, we get $\left[\frac{1}{2}(a+b-c)\right]^{2}$. Therefore, $\left.S_{\triangle C P Q}=S_{\text {quadrilateral OECF }}\right)$