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## Homework Statement

If the method of undetermined coefficients is used to find a particular solution

yp (t) to the differential equation y'''-y'=te^(-t)+2cos(t) should

have the form: ?

## Homework Equations

## The Attempt at a Solution

LHS

r^3-r=0

roots= 0, 1

y_c(t)=c_1e^t

RHS

te^(-t)+2cos(t)

(At+B)e^(-t)+Ccos(t)+Dsin(t)

correct answer given however is

t(At + B)e^(-t) + C cos(t) + D sin(t)

I don't know how that t in front got there.. It would make sense if my LHS gave e^-t. but i dont think it does.

Thanks