Nondimensionalize the pendulum equation:

$\frac{d}{(d)t}=$;$,\frac{d}{(d)t}=-\frac{mgsin+L}{mL}.$

By introducing the dimensionless variable t$*=$ t$/$T$,$ where T is a conveniently chosen time scale constructed out of the parameters m$,$g$,$ and zeta. For small angles, the equation simplifies: sintheta ~ theta. Then the equation becomes linear in theta with constant coefficients, so you know that its solution is some sort of exponential in time. Solve the equatio of motion using this approximation.