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**Alfred****Guest**

I'm new to sigma notation and I'm supposed to put 3 + 6+ 12+ 24 + 48 in it, but I really can't figure out how to do it. I've tried for so long, but nothing I try works. Can come help?

**MajikWaffle****Member**- Registered: 2005-12-14
- Posts: 11

n <- end of the sequence

Σ (Equation)

k = 1 <- starting

*Last edited by MajikWaffle (2005-12-14 17:57:43)*

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**Alfred****Guest**

I know all that, it's just this problem I can't get.

**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

Don't ask me how I got this, I couldn't tell you. Just a bunch of guessing and checking:

Summation of k = 1 to n of 2^(k+1) - 2^(k-1)

*Last edited by Ricky (2005-12-14 18:11:14)*

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**Alfred****Guest**

I couldn't get that to work out. Are you sure?

**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

2^(k+1) - 2^(k-1)

K = 1:

2^2 - 2^0 = 4 - 1 = 3

K = 2:

2^3 - 2^1 = 8 - 2 = 6

K = 3:

2^4 - 2^2 = 16 - 4 = 12

K = 4:

2^5 - 2^3 = 32 - 8 = 24

And so on.

*Last edited by Ricky (2005-12-14 18:17:51)*

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,631

Is this it?

`[math]\sum_{k=1}^\infty2^{k+1}-2^{k-1}[/math]`

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**ryos****Member**- Registered: 2005-08-04
- Posts: 394

I think this one is cleaner:

El que pega primero pega dos veces.

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**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

ryos, what's n?

And where can I look up commands for this code?

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,631

It is "LaTeX" and I don't know it very well.

Just found this though

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**ryos****Member**- Registered: 2005-08-04
- Posts: 394

n is the number of iterations.

El que pega primero pega dos veces.

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