Attachment 21321

Above is my problem sorry that it's a link but It was to hard to convert from latex into here (i used some packages)

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- Mar 31st 2011, 06:56 PMfizzle45ODE Method of Variation of Parameters help
Attachment 21321

Above is my problem sorry that it's a link but It was to hard to convert from latex into here (i used some packages) - Apr 1st 2011, 04:58 AMJester
You're missing a term in your variation of parameters formula. Given an nth order linear ODE

$\displaystyle a_n(x)y^{(n)} + a_{n-1}(x)y^{(n-1)} + \cdots + a_1(x)y' + a_0(x)y = f(x)$

with independent solutions $\displaystyle y_1, \cdots , y_n$ the variation of parameters formula is

$\displaystyle \displaystyle y_p = \sum_{k=1}^n y_k \int \dfrac{W_k}{W} \dfrac{f(x)}{a_n(x)}dx$.

With what you have you set $\displaystyle a_n = 1$ where it should be $\displaystyle a_n = x^3$. With this assignment things work out giving you the desired $\displaystyle y_p$.