sorry, i am new to this forum...
yp = Ce-x(Acos x + Bsin x). insert a constant at e-x since it is one of the members of undetermined coefficient?
2y'' + 4y' + 7y = e-xcos x <this is the original question and the answer for yp is 1/3(e-xcos x). Still i could not manage to get the ans for yp...