calculus

\sum_{n=0}^{\ \propto }{1/(3n+1)-1/(3n+2)}

8 Answers

66
kaymant ·

The answer:
\dfrac{2\sqrt{3}\ \pi -9}{18}

341
Hari Shankar ·

I get \frac{1}{3} \left(1+\ln 3 + \frac{\pi \sqrt 3}{6} \right ) by a somewhat illegitimate procedure :D

39
Dr.House ·

just solved this power series and infinite series topic for today`s test.

can u please say wat was your illegitimate prceedure so that i may also try !

(btw i din get this by watever means i know from clg stuff so far)

66
kaymant ·

Sorry, the answer should be
\dfrac{\pi}{3\sqrt{3}}
In #2 I calculated the sum from n=1 onwards. So we get the result by adding 1/2 to it.

341
Hari Shankar ·

@L: I started with expansion of \frac{1}{1-x^3}

Then integrated w.r.t x between limits 0 and t

Then integrated w.r.t t between limits 0 and 1

I've made an error in calc, but a log term is likely to b there

66
kaymant ·

@theprophet
You have indeed made a mistake in the calculations. That integration gives \dfrac{\pi}{3\sqrt{3}} and no log terms.

341
Hari Shankar ·

then its fine.

For us non-students a brief sketch of the solution is permitted leaving the rest as an easy exercise for the students :D

341
Hari Shankar ·

You must write that correctly. I meant

\lim_{t \rightarrow 1^-} \int_0^t \left(\int_0^x \frac{1}{1-x^3} \ dx \right) \ dt

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