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JKreutz
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Hi, guys. For an E&M/quantum mechanics problem I have to integrate the series below:
Integrate
[itex]\int{r^{2}e^{y r} \, dr}.[/itex]2. The attempt at a solution
Using integration by parts and and "differentiating under the integral" give the same answer:
[itex] I= \frac{2 e^{yr}}{y^{3}}-\frac{2 r e^{yr}}{y^{2}}+\frac{r^{2} e^{yr}}{y} + C [/itex],
where I is the solution to the integral and C is an arbitrary constant. I'd read about Newton trying to integrate infinite series, so I thought as a check and out of curiosity I'd express the integrand as an infinite series and integrate each term. Specifically I expressed exp(yr) as a Maclauren series, multiplied each term by the [itex]r^{2}[/itex] and used the "power rule" to get
[itex]I=\sum_{n=0}^{\infty} {\frac{y^{n} r^{(n+2)}}{n! \, (n+3)}}. [/itex]
I can't see how this series could represent the other answer I found. Moreover, I've never seen this done before and I don't know to look up this kind of information. (Googling "Infinite Series and Integrals" was not helpful ><). Any help would be appreciated.
Homework Statement
Integrate
[itex]\int{r^{2}e^{y r} \, dr}.[/itex]2. The attempt at a solution
Using integration by parts and and "differentiating under the integral" give the same answer:
[itex] I= \frac{2 e^{yr}}{y^{3}}-\frac{2 r e^{yr}}{y^{2}}+\frac{r^{2} e^{yr}}{y} + C [/itex],
where I is the solution to the integral and C is an arbitrary constant. I'd read about Newton trying to integrate infinite series, so I thought as a check and out of curiosity I'd express the integrand as an infinite series and integrate each term. Specifically I expressed exp(yr) as a Maclauren series, multiplied each term by the [itex]r^{2}[/itex] and used the "power rule" to get
[itex]I=\sum_{n=0}^{\infty} {\frac{y^{n} r^{(n+2)}}{n! \, (n+3)}}. [/itex]
I can't see how this series could represent the other answer I found. Moreover, I've never seen this done before and I don't know to look up this kind of information. (Googling "Infinite Series and Integrals" was not helpful ><). Any help would be appreciated.
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