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I'll make my question short, I am encountering a error when doing expansion. I am expanding $f(x)=2x^3+4x+1$ and after the expansion, things don't match.

Here's what I'm doing.

Let $a=5$



And I immediately realize that the coefficient for $x^3$ is wrong.

Am I misunderstanding how to use Taylor series or my calculation just sucks?

Thanks in advance!

share|improve this question
$f'''(x)\equiv 12$, so $f'''(5)=12$, not $60$. –  njguliyev Sep 29 '13 at 18:11
@njguliyev I'll go kill myself, I'm sorry for posting stupid question here. You wanna post it as an answer or delete it? –  Shane Hsu Sep 29 '13 at 18:13
@njguliyev : Post it as an answer. –  Patrick Da Silva Sep 29 '13 at 18:14
@ShaneHsu We all make mistakes sometimes, don't be dramatic. –  Pedro Tamaroff Sep 29 '13 at 19:08

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