Solution
= Solution
The preceding formulas give
$$
\frac c{c_g}=\frac{c^2}{c_s^2}
=1+\frac{\omega_n^2}{c_s^2\kappa^2}.
$$
Therefore
$$
\boxed{c=mc_g,\qquad
m=1+\left(\frac{(2n+1)\pi}{2\kappa h}\right)^2>1}.
$$
= Solution
The preceding formulas give
$$
\frac c{c_g}=\frac{c^2}{c_s^2}
=1+\frac{\omega_n^2}{c_s^2\kappa^2}.
$$
Therefore
$$
\boxed{c=mc_g,\qquad
m=1+\left(\frac{(2n+1)\pi}{2\kappa h}\right)^2>1}.
$$