Find particular solution third order Diff Eq

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SUMMARY

The discussion focuses on solving the third-order differential equation y''' - y = e^x + 7. The user attempts to find a particular solution using the method of undetermined coefficients, initially proposing y = Ae^x + B and later adjusting to y = Ax^2e^x + Bx^2 due to repeated roots in the complementary solution. The correct approach involves recognizing that the particular integral for e^x should be xe^x, necessitating a revision of the complementary solution to account for one real root and two imaginary roots derived from the auxiliary equation r^3 - 1 = 0.

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Herricane
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Homework Statement



y''' - y = e^x + 7

Homework Equations





The Attempt at a Solution



I used y=Ae^x +B and then I multiplied by x^2 because y_c = c1 + c2 e^x + c3 e^(-x)

the c1 and c2 e^x value repeat. Therefore I got: y= Ax^2 e^x + Bx^2

I got A = 0 and A=1 which is wrong and B=0

Any hints? do I need to add a Cx e^x and then multiply by x^2?
 
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Your auxiliary equation would be r^3-1=0 which would lead to only one real root and two imaginary roots.

Since e^x is on the right side, the particular integral for the e^x on the right would be xe^x.

You will need to change your complementary solution y_c to reflect one real root and two imaginary roots.
 

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