Đáp án:
$\begin{array}{l}
\Delta D{\rm{EF = }}\Delta {\rm{MNP}}\\
\Rightarrow \left\{ \begin{array}{l}
EF = NP\\
FD = MN\\
DE = MP = 3cm
\end{array} \right.\\
mà:\,\left\{ \begin{array}{l}
EF + FD = 10\\
NP - MP = 2
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
NP + FD = 10\\
NP - 3 = 2
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
NP + FD = 10\\
NP = 5
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
FD = 10 - NP = 5\\
NP = EF = 5\left( {cm} \right)
\end{array} \right.\\
Vậy\,EF = NP = 5\left( {cm} \right);FD = MN = 5\left( {cm} \right);DE = MP = 3cm
\end{array}$
