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    Help me this question.
    geometric progression
    a3 = 16, a4 = 12.8, find a and r
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    \displaystyle r=\frac{a_4}{a_3}
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    i get it thanks xD

    Sn = 2(2n-1)-2 find a and r
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    (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
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    (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.
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    (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 ?
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    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?
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    (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?
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    \displaystyle\sum_{k=3}^8 {k^2-1}\

    There is a formula for the sum of k2 it's covered in FP1, what level of maths do you do?
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    (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
    \displaystyle \sum_{k=2}^9 (k^2-1)=\sum_{k=2}^9 k^2 -\sum_{k=2}^9 1=
    \displaystyle \sum_{k=1}^9 k^2 -1^2-8=\sum_{k=1}^9 k^2 -9
    And as it known
    \sum_{k=1}^n k^2=\frac{n\cdot (n+1)\cdot (2n+1)}{6}
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    (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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