A question on undetermined coefficients

  • Thread starter shemer77
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Homework Statement


http://gyazo.com/6c440aa92106f729639c91f6d59dcd89


The Attempt at a Solution


My question is why is yp = At^3+Bt^2 +Ct. The reason I ask that is because is see t^2+2t so why wouldnt it be yp=At^2 +Bt +c?
 

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SammyS
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Homework Statement


http://gyazo.com/6c440aa92106f729639c91f6d59dcd89

The Attempt at a Solution


My question is why is yp = At^3+Bt^2 +Ct. The reason I ask that is because is see t^2+2t so why wouldn't it be yp=At^2 +Bt +c?
attachment.php?attachmentid=48917&stc=1&d=1341594524.png


Because (D3 + 4D)( At3+Bt2 +Ct) = 12At2 + 8Bt + 6A + 4C .

Whereas, (D3 + 4D)( At2+Bt+C) = 8At + 4B, which is not a quadratic.

.
 

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