I'm not currently in a class, but I'm doing this for fun.. but technically I would still call it coursework, so I'm posting it here.. I'm studying Redheffer/Sokolnikoff's Mathmatics of Modern Engineering.. and I find a problem on page 75, use the method of variation of parameters to find the solution of this equation: Y` + 3Y = X^3 this one is easy enough to find the forced response by plugging in Y= AX^3 + BX^2 + CX + D = X^3, and equating the coefficients. The coefficients turn out to be A=1/3, B=-1/3, C=-2/9, D=-2/27. This is the answer, but that's not my problem. The variation of parameter method discussed in this section requires two linearly independant solutions to the homogenous equation,, of which I can only find one: Y= Ke^(-3t). Of course there is the trivial solution, but that would make the Wronksian in the denominator of the integrals zero. For the life of me, I can't see how in the world one can use the variation of parameters method to solve this.. Is it perhaps a trick question? I'd email Sokolnikoff.. but he's long since left the world.. any ideas?