Hello, First here is the question that I am supposed to solve: Solve the following nonhomogeneous differential equations: b) y'' + 2y' + 2y = e^-x c) 2y'' + y' = cos 2x. I am supposed to be using the method of variation of parameters to solve these equations. What my problem is I end up getting to a point where I have two equations in which I should be able to solve for the derivative of parameter one (u'sub1) and the derivative of parameter two (u'sub2). Unfortunately I am getting stuck. And I am not sure why. For b) I have the following two equations: u'sub1 ysub1 + u'sub2 ysub2 = 0 = u'sub1 e^-x + u'sub2 xe^-x and the particular equation u'sub2 - u'sub2 x + usub2 x - u'sub1 + usub1 = 1 From these I am supposed to find u'sub1 and u'sub2 and eventually come to find usub1 and usub2. Now when I solve for u'sub1 e^-x + u'sub2 xe^-x = 0 I get u'sub1 = (-u'sub2 xe^-x)/e^-x = -u'sub2 x I then sub. into the other equation for u'sub1 u'sub2 - u'sub2 x + usub2 x - u'sub1 + usub1 = 1 becomes u'sub2 - u'sub2 x + usub2 x + u'sub2 x + usub1 = 1 which becomes u'sub2 + usub2 x + usub1 = 1 But I am stumped here. How do I solve for u'sub2 when I still have usub2 and usub1? I know I am missing something incredibly obvious. I just can't seem to know what. For question b) I am having similar problems - still trying to solve for u'sub1 and u'sub2. Update: I have figured out question c). I am still working on part b however. 2nd Update: I figured out question b as well. Thanks to all who took the time to look at my post. Cheers.