y'''' -6y'''+9y''=x

i take y_p=ax+b

i get 0=x

so i cant find the a ,b for the solution

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- Dec 8th 2010, 07:25 AMtransgalacticparticular solution of high order 2d
y'''' -6y'''+9y''=x

i take y_p=ax+b

i get 0=x

so i cant find the a ,b for the solution - Dec 8th 2010, 07:40 AMTheEmptySet
Your characteristic equation is

$\displaystyle r^4-6r^3+9r^2=0 \iff r^2(r-3)^2$

so the complimentary solution already contains $\displaystyle y=ax+b $

Since there is a factor of $\displaystyle r^2$ you must multiply your guess by $\displaystyle x^2$ to get $\displaystyle ax^3+bx^2$ - Dec 8th 2010, 11:08 AMtransgalactic
what are they laws tieing the homogeneus and the practical solutions?

i we have also (r-3)^2 thing

why its not changing the particular solution too

?

whats the general theory on think link thing

?

i dont know how to search it on google - Dec 8th 2010, 02:23 PMTheEmptySet
Try this link, it may help.

The Method of Undetermined Coefficients

Also try google Method of undetermined coeffients.