Use a method similar to that suggested in Problem 10 to show that the eigenvalue problem...

Use a method similar to that suggested in Problem 10 to show that the eigenvalue problem in Problem 6 has no negative eigenvalues.

Reference of Problem 10:

Prove that the eigenvalue problem

has no negative eigenvalues. (Suggestion: Show graphically that the only root of the equation tanh z = -z is z = 0.)

Reference of Problem 6:

Consider the eigenvalue problem