Đáp án:
Theo Pytago ta có:
$\begin{array}{l}
A{B^2} + A{C^2} = B{C^2}\\
\Rightarrow B{C^2} = {9^2} + {12^2} = {15^2}\\
\Rightarrow BC = 15\left( {cm} \right)\\
Do:\frac{{DA}}{{AB}} = \frac{{DC}}{{BC}}\\
\Rightarrow \frac{{DA}}{9} = \frac{{DC}}{{15}} = \frac{{DA + DC}}{{9 + 15}} = \frac{{AC}}{{24}} = \frac{{12}}{{24}} = \frac{1}{2}\\
\Rightarrow \left\{ \begin{array}{l}
DA = 4,5\left( {cm} \right)\\
DC = 7,5\left( {cm} \right)
\end{array} \right.
\end{array}$