$K$ is any point on side $\overline{BC}$ of triangle $\triangle ABC$ . Find the length of the common chord of the nine-point circle of triangle $\triangle ABK$ and triangle $\triangle AKC$ if $\overline{AK} = 10$.
$K$ is any point on side $\overline{BC}$ of triangle $\triangle ABC$ . Find the length of the common chord of the nine-point circle of triangle $\triangle ABK$ and triangle $\triangle AKC$ if $\overline{AK} = 10$.