Foo - calc help pretty please

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View Full Version : calc help pretty please

cnickgo
12-10-07, 06:42 PM
Ok guys im stuck on one correction, and I have to turn this in before I take my exam at noon tommorow. Dealing with series:

the series: sum from n=1 to infinity 1/n3^n
I know it converges (the book says so!), how do I show that and find the upper and lower limits?

Please some bored and benevolent engineer/physicist/mathematician or any other calculus saavy person help me out. I need to move on and study other classes.

Air
12-10-07, 07:01 PM
Two hints:

1. Graph it.

2. Plug in some numbers into the equation and note where they seem to converge to.

jschen
12-10-07, 07:46 PM
What is n3^n? It would be helpful if you would use parentheses or whatever else it took to make it absolutely unambiguous what you're trying to write.

And what have you tried so far?

cnickgo
12-10-07, 07:58 PM
What is n3^n? It would be helpful if you would use parentheses or whatever else it took to make it absolutely unambiguous what you're trying to write.

And what have you tried so far?

sorry 1/ n*(3^n)

I know it's not a geometric series, can't be p-test or ratio rest, i could compare it with most anything but that wouldn't give the specific bounds I need, and as far as the integral-test maple spit out an imaginary answer and I can't find a simple solution to that either.

Falkon
12-10-07, 09:52 PM
is that 1/n 3^n or 1/(n3^n)?
if it's the latter, here's a hint. Your first step is the divergence test. Take the limit.
Why can't you use the ratio test? Work it on paper, and tell me what you get.

soma5
12-10-07, 11:11 PM
Series with nth term 1/(n*(3^n)) converges by comparison to the geometric series where the nth term is 1/(3^n) because the denominator is larger.

-soma5

EJ123
12-11-07, 05:36 AM
What the foo is this? I'm just in meager pre-cal, whew.

Falkon
12-11-07, 10:12 AM
Following up. Do the ratio test and take the limit.

eofelis
12-11-07, 10:14 AM
I took my calc II final yesterday. It killed me. Hoping for a passing grade in the class...