Please help me with the following eigenvalue problem:

X"(9:) = AX(:E), for a: E [0, L] X(0) = 0,X(L) = 0. Find the values of L for which /\\ = 10 is an eigenvalue (that is the equation X \" = 10X with boundary conditions X (0) = X (L) = 0 has non trivial solutions)