Solving ODE which is a sum of Biharmonic and laplace DE

Dear all,

I am looking for solution of ODE with variable coefficients. The form of the equation is as follows:

Bi-harmonic-equation+ Constant * Laplace-equation = 0, which is can be written as

D^{4} w+ C* D^{2}w=0

where D^{4}= D^{2}*D^{2}, where the differential operator D^{2}= d^{2}/dx^{2} + 1/r d/dx

Since I am new I am not able to type in proper mathematical format for easy understanding.

operator D^{4} is equation (7) in the following link.

Biharmonic Equation -- from Wolfram MathWorld

and operator D^{2} is equation (3) in the following link.

Harmonic Function -- from Wolfram MathWorld

Could any one give me inputs for general solution to this differential equation.

Thanks.