Using the broken-line hypothesis the stability differential equation is written in terms of a deflection function \(\chi\), the derivatives of which specify the lateral displacement w. The solution is sought in the form \(\chi(r,\Theta)=\chi_ 0(r)\cdot \cos n\Theta,\) where \(\chi_ 0(r)\) is expanded in a power series. The introduced boundary conditions yield a system of homogeneous algebraic equations, the eigenvalues of which determine the buckling load. Examples are calculated for clamped and simply supported edges as well as for a homogeneous and a sandwich plate.