how to apply separation of variable of 2d wave equation in polar coordinates? can u explain the follwing question?

Circular Drum The two-dimensional wave equation 1 1 1 5832.: = gar tram} + 7263\". (41 governs small displacements, u = u(r,3,t) of a circular drum. The coordinate 1' represents the radial direction1 and 6' represents the angular direction. We want clamped boundary conditions on the outer radius, 1:,{1' = n.3,t] = . [5] Copyright 2017 The University of Sydney 1 Question 2(a): Solve for the time-periodic characteristic modes of equation (4] using separation of variables. That is! nd \"(a 5'11?) = names\