By constructing the one-dimensional Green’s function solve the
inhomogeneous equation \[ \frac {d^2u}{dx^2}=f(x),\qquad u(0)=\alpha ,\qquad u(1)=\beta . \]
Use Green’s functions to solve \[ \frac {d^2u}{dx^2}-\alpha ^2u=f(x)\quad \text {on }L^2(-\infty ,\infty ) \] with \(\alpha \) real.