How to evaluate sigma notation

2011 11 22
3 个回答
4 次查看（30 天）

0 个投票

Hi everyone! I am completely new to Matlab and am in need of great help.
I have to find the algebraic sum of (n sigma i=1) (5/n) ((5i/n)^4 + 5(5i/n)^2 + 5i/n)
I am totally lost. Thank you so much if you can help!

1 个评论
显示 -1更早的评论 隐藏 -1更早的评论

Jan
Jan 2011-11-22
The shown notation is not clear. Which are the limits of the sum?

请先登录，再进行评论。

请先登录，再回答此问题。

回答（3 个）

Jan
Jan 2011-11-22

0 个投票

For homework questions the usual proceding is, that you show, what you have done so far and ask a specific question. Then you have the chance to submit the solution without cheating.
Yuna Kim
Yuna Kim 2011-11-22

0 个投票

Well, ultimately the question is asking to take the sum to infinity so n isn't defined but the initial question is to express the area under the curve y=x^4 + 5x^2 + x from 2 to 7 as a limit.
I'm asking for part b which asks to use a computer algebra system (matlab) to evaluate the sum in part (a).
Btw, thanks for asking!
Walter Roberson
Walter Roberson 2011-11-22

0 个投票

syms i n
symsum(5*((5*i/n)^4..., i, 1, n)
However, this does not appear to have anything to do with that integral.

2 个评论
显示 无 隐藏 无

Yuna Kim
Yuna Kim 2011-11-22
We have to ultimately take the limit to infinity to find the actual sum. I did everything by hand already but have to show it through matlab as well, which is what I am having trouble with. I should be able to find the area if I take the limit to infinity.
I have entered limit (3125/n^4 - 625/n^2 + (25*sqrt(-1))/n, n, infinity) but it is giving me zero which makes me think that I got the summation wrong.
Am I doing something wrong?
Yuna Kim
Yuna Kim 2011-11-22
also i^2 should equal n(n+1)(2n+1)/6 and so on.

请先登录，再进行评论。

类别

在 帮助中心 和 File Exchange 中查找有关 Matrix Indexing 的更多信息

标签

提问:

Yuna Kim
Yuna Kim
2011-11-22

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by