Method of Undetermined Coefficients

jmg498
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I am looking for the form of a solution for a second order ODE with right hand side: x (sin x + 2)

I'm thinking the form would be (Ax + B) sin(x) + (Cx + D) cos(x) + Ex + F. Does this seem correct?

Thanks for any help or suggestions!
 
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Have you tried it? That would tell you whether it is correct or not! If it is correct, you will get an answer. If it is not correct, you won't.

Actually, it is impossible for us to tell because you haven't given us the homogeneous equation or its solutions. If sin(x) or cos(x) or x sin(x) or x cos(x) are already solutions to the homogenous equation, you will need to multiply (Ax+B)sin(x) and (Cx+ D)cos(x) by x again. If x or a constant is already a solution to the homogeneous equation, you will need to Ex2+ Fx.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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