Find Sn= (n-1) above r=0 under 3^r

help me please!

**0**

# sigma notation

Started by Hev, Feb 28 2007 08:10 PM

3 replies to this topic

### #1

Posted 28 February 2007 - 08:10 PM

This year's Fenella Feline (CAT) in Peterhead's Pantomine Pinocchio!

### #2

Posted 01 March 2007 - 09:00 PM

OK, first of all just a general thing about the notation. It's nothing special! All means is:

When the number on top of the is finite (i.e. not ) this is called a partial (or finite) sum.

There are two special types of sequences: arithmetic and geometric. For these we have formulae for the

You can check to see if the terms come from a geometric sequence by dividing any term by the term immediately before it. It is a geometric series if this number is the same no matter which term you do this for. This number is called the common ratio.

In our case, . So the common ratio is .

The formula for the sum to

where

Does this help?

When the number on top of the is finite (i.e. not ) this is called a partial (or finite) sum.

There are two special types of sequences: arithmetic and geometric. For these we have formulae for the

*n*th partial sum.You can check to see if the terms come from a geometric sequence by dividing any term by the term immediately before it. It is a geometric series if this number is the same no matter which term you do this for. This number is called the common ratio.

In our case, . So the common ratio is .

The formula for the sum to

*n*terms where the terms come from a geometric sequence is:where

*r*is the common ratio and the first term of the sum is*a*. In our case .Does this help?

### #3

Posted 01 March 2007 - 11:52 PM

yeah i got it all now thanks

think i was just far too tired for maths.

know the feeling? haha

think i was just far too tired for maths.

know the feeling? haha

This year's Fenella Feline (CAT) in Peterhead's Pantomine Pinocchio!

### #4

Posted 04 March 2007 - 06:24 PM

Certainly do

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