y" + y = sin(x) 1. The problem statement, all variables and given/known data Solve y" + y = sin(x) for y=y(x) using the method of undetermined coefficients 2. Relevant equations 3. The attempt at a solution The homogeneous solution Yh = Asin(x) + Bcos(x) The particular solution Yp = Csin(x). Y''p = -Csin(x) Y''p + Yp = -Csin(x) + Csin(x) = 0 No C exists to make Y''p + Yp = sin(x) for all x What am I doing wrong?