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# Sequences and Series C2 Watch

1. Help me this question.
geometric progression
a3 = 16, a4 = 12.8, find a and r
2. i get it thanks xD

Sn = 2(2n-1)-2 find a and r
3. (Original post by NKenny)
i get it thanks xD

Sn = 2(2n-1)-2 find a and r
from this question I don't understand this bit.

ak is k term
and Sn is sum of n term

both is the term but why is it have 2 different letter
4. (Original post by NKenny)
from this question I don't understand this bit.

ak is k term
and Sn is sum of n term

both is the term but why is it have 2 different letter
k refers to a particular term. There are a total of n terms.
5. (Original post by Mr M)
k refers to a particular term. There are a total of n terms.
so S4 = a1+... +a4 rite ?

and what about geometric progression and geometric series. are they the same thing ?
6. Could anyone give me a hand with some sigma notation?

I am supposed to find the sum of 8 terms starting from term 3 with the general formula of (k^2-1), is this Geometric or Arithmetic? can i use the formula's or do i have to work out each term and add them?
7. (Original post by SebastianTindall)
Could anyone give me a hand with some sigma notation?

I am supposed to find the sum of 8 terms starting from term 3 with the general formula of (k^2-1), is this Geometric or Arithmetic? can i use the formula's or do i have to work out each term and add them?
Is this what you wanted?
Spoiler:
Show

There is a formula for the sum of k2 it's covered in FP1, what level of maths do you do?
8. (Original post by SebastianTindall)
Could anyone give me a hand with some sigma notation?

I am supposed to find the sum of 8 terms starting from term 3 with the general formula of (k^2-1), is this Geometric or Arithmetic? can i use the formula's or do i have to work out each term and add them?
Your first term is 3 so k=2 (2^2-1=3)
For the last term k=9
THe question is

And as it known
9. (Original post by NKenny)
and what about geometric progression and geometric series. are they the same thing ?
Here is an example of a geometric progression:

1, 2, 4, 8, 16, 32

Here is an example of a geometric series:

1 + 2 + 4 + 8 + 16 + 32

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