Can somebody explain Sigma problems/equations to me?

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Omnis

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This wonderful little greek letter is giving me an algebraic headache.

How the hell does a Sigma work for series equations and everything?
 
Agreed Kylehnat.
That's a little vague Omnis, but I'll give it a shot.


I think you mean a 'Σ'

It's a summation symbol. You sum the items of the series following it.

Beneath it you'll usually have something like x=i, where i is an integer, x a variable. Above you'll have another integer, j. i is the lower bound for x, and j is the upper bound.

Begin by setting all x's in the equation to the value i, and add to it the result of the equation of x=(i+1), then x=(i+2), x=(i+3), ..., x=j


For example,
Code:
5
Σ (x+x^2 +1)
x=2
for x=2, you get 7
for x=3, you get 13
for x=4, you get 21
for x=5, you get 31
stop there

the answer to the summation is then 72


Forgive me if I'm missing the point here. Maybe you're talking about the use of the summation symbol in infinite series (ie, MacLaurin/Taylor, power, Fourier, etc) - if so, I can try to explain that later for you. The usage in such a situation is the same though. It is used to write an infinite series in a more compact form, usually by setting the upper bound, j, to infinity.
 
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I looked up the wikipedia article on them. It helped. I guess I was absent the day my teacher taught about them, and now that I'm finishing nightschool, I find the sigma problems gave me the most trouble and I need some clarity before I go taking the final test.

Okay, BL, thanks. That helps a lot. The problem with the software the night school uses is that their section on series is very vague. The problems given are a mixture of simple summations (like the ones done), infinite series, etc. The sigmas also gave me headaches when doing correlation work.

I'll learn through wikipedia and other websites anyway, but I thought GTP would be a good stop just to soak up any kind of help and explanation.

I'm sorry for the vagueness of this, but I can't really ask for answers when even the question is not yet clear.
 
Ya, just a summation.

See my above post, but ignore that last paragraph about infinite series. Given my example, and the one you posted you should certainly figure it out.
 
If it helps, I've found that sigmas are easier to work out in individual steps than all at once, finding the solution to each set and then adding them together afterwards.
 
Yeah, the only sigma that came to my mind was that pesky variance from statistics. I forgot all about series. Fancy-schmancy adding...

The real fun with series begins in calculus. Boundary Layer has given a little teaser of the fun that awaits :D.
 
I completely forgot how to do those (its the summer :D), but i remember some situation where the top number would be infinite or something like that. I don't think i had to much trouble with that, logs were what sucked for me :grumpy:

EDIT: I think the infinite happened in geometric summation. *Looks at math notes completely oblivious on how to do any of it* god im worried about trig now :scared:
 
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