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Differential equations, variation of parameters

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Homework Statement


Using variation of parameters, find the general solutions of the differential equation


Homework Equations


y''' - 3''y + 3y' - y = et / t
where et/t = g(t)


The Attempt at a Solution


I know how to solve these types of equations when its a second order, but I don't understand what to do for the particular solution since there are 3 solutions to the associated homogeneous equation, y1 = et, y2 = tet, y3 = t2et.
Usually I would just take the 2 solutions and compute the Wronskian, then use the formula where it's -y1*integral([y2*g(t)]/W)dt + y2*integral([y1*g(t)]/W)dt.
Since there are three solutions though, I don't understand how to solve it. My textbook uses a different method where they use something like v1'y1 + v2'y2 + v3'y3 = 0, v1'y1' + v2'y2' + v3'y3' = 0, and then the next equation is the same except the y's are the 2nd derivatives and it = g(t).
Then they solve for v1, v2 and v3, integrate, and plug them into the homogeneous equation to get the particular solution.
Sorry if this isn't clear!
 

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