An Alternative Method for the Undetermined Coefficients and the   Annihilator Methods
  This paper exhibits a very simple formula for a particular solution of a linear ordinary differential equation with constant real coefficients, P(d/dt)x = f, f a function given by a linear combination of polynomials, trigonometrical and exponential real functions products. This is done by solving lower triangular linear systems with constant coefficients. Two examples are given. 
Oswaldo Rio Branco de Oliveira
math.CA