1. The problem statement, all variables and given/known data http://i.imgur.com/01AUp.png 2. Relevant equations 3. The attempt at a solution Having some problems with this question, using a third + first order nonlinear device to make a multiplier. I'm fine with using a second order, but this one is stumping me. So, I take x(t) = m(t) + cos(wt) and plug it into x(t) + (x(t))^3 , and I get (expanding cos(wt)2 and cos(wt)3 terms: 5/2* m + cos(wt) + m^3 + 3* m^2* cos(wt) +3/2m cos(2wt) + 3/4* cos(wt) + 1/4* cos(3wt). Problem: None of the terms contain m(t)cos(wt)! Then what am I supposed to filter out?