Solution (source code)

= Solution

For each spatial <normal mode>, the temporal equation is $T_n''+\omega_n^2T_n=0$, with <angular frequency> $\omega_n=ck_n=cn\pi/L$. Hence
$$
\boxed{T_n(t)=A_n\cos(\omega_nt)+B_n\sin(\omega_nt).}
$$
The ordinary <frequency> is $\omega_n/(2\pi)=cn/(2L)$; it should not be confused with the angular frequency used in the sine and cosine arguments.