Three. (20 points) Given that the perimeter of right triangle $\triangle ABC$ is 14, and its area is 7. Try to find the lengths of its three sides.

 untranslated part:
(20 分) 已知 Rt $\triangle A B C$ 的周长为 14 , 面积为 7. 试求它的三边长.

Here is the translated text with the format preserved:

Three. (20 points) Given that the perimeter of right triangle $\triangle ABC$ is 14, and its area is 7. Try to find the lengths of its three sides.
Three, let the three sides of $\triangle A B C$ be $a, b, c$, where $c$ is the hypotenuse. According to the problem, we have the system of equations:
$$
\left\{\begin{array}{l}
a+b+c=14, \\
\frac{1}{2} a b=7, \\
a^{2}+b^{2}=c^{2} .
\end{array}\right.
$$

From equation (1), we get $a+b=14-c$.
Thus, solving gives $c=6$.
Therefore, $a+b=14-c=8, a b=98-14 c=14$.
Hence, $a, b$ are the roots of the equation $z^{2}-8 z+14=0$.
Solving gives $z=4 \pm \sqrt{2}$.
Thus, the three sides of the right triangle $\triangle A B C$ are $4-\sqrt{2}, 4+\sqrt{2}, 6$.