Toronto Math Forum
MAT2442018F => MAT244Lectures & Home Assignments => Topic started by: Weina Zhu on October 08, 2018, 10:37:22 AM

during solving the general solution for the nonhomogeneous equation, why should we guessing an answer combine sin&cos together for
an equation like the righthand side only contains one of the sin&cos.
Thanks!

Because derivative of sine is cosine and v.v. Try to solve $y''+y'=\cos(x)$ as with $y=a\cos(x)$.