2008-II-24
Ans: A
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Note that
$\begin{array}{rcl}
AC^2 + BC^2 & =

Note that
$\begin{array}{rcl}
AC^2 + BC^2 & =

Let $\angle ADC = y$. Add a point $E$ on $AB$ such that $E

Add a horizontal line and the line divides $b$ into $b_

According to the above figure, we have
$\begin{array
$\begin{array}{cl}
=
$\begin{array}{cl}
= &
$\begin{array}{rc
