1. The problem statement, all variables and given/known data y''+[tex]\lambda[/tex]y=0 y'(0)=0 y'(pi)=0 2. Relevant equations 3. The attempt at a solution What's puzzling me is the case when we check if the eigenvalue is zero. y''=0 y'=C1 y=C1x+C2 Now when I check the first boundary value I get C1=0 now How do I check the second one ? with the pi... It doesn't make sense plugging into the first derivative again because I have no x value (only a constant). The answers show this: lambda=0 is an eigenvalue and the general solution is y0(x)=1 How did they get this ? Thanks.