I am new to this forum but I am preparing my graduation exam. I can not solve this question and I have been trying for the last 2 days AND NIGHTS. A friend of mine recommended this forum and I was hoping perhaps you guys could help me out, it involves the following problem;

d^2a/dx^2 = f(x)

a(0) = 0

da/dx + ha(L) = 0, at X=L

I have tried integrating directly but I can not get a nice answer. I also need to solve using the variation of parameters and write in a green's function. However, I keep getting terms which I can not possibly put into a symmetric green's function. Can someone please please please help me out here?

Thanks a lot

Greetings from Bulgaria