Question

Please prove that N1T1=N2T2 for simple pendulum

Answer 1

The time of a single oscillation t (period) can be found as total time T of N oscillations divided by N:

$$t=T/N.$$

For the same simple pendulum, the period is constant:

$$t=T_1/N_1=T_2/N_2=...=\text{const}.$$