Regular Sturm

For what Values of x1 are there infinitely many solutions to the boundary value problem y"+y = 0, y(0) = 0, y(x1) = 0.

For what values of x1 are there infinitely many solutions to the boundary value problem y" + y = 0, y(0) = 0, y(x1) = 0.

For what values of alpha are there infinitely many solutions to the boundary value problem y" + ay = 0, y(0) = 0, y( pi ) = 0.