  We give a simple solution of the equation d/dx(pdu/dx)+qu=cu whenever a
nontrivial solution of d/dx(pdu/dx)+qu=0 is known. The method developed for
obtaining this result is based on the theory of pseudoanalytic functions and
their relationship with solutions of the stationary two-dimensional Schrodinger
equation. The final result, that is the formula for the general solution of the
equation d/dx(pdu/dx)+qu=cu has a simple and easily verifiable form.
