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    I have a couple of questions that I'm stuck on, wondering if anyone can help....

    1.
    10
    ∑ 2r - 3
    r=1

    i have to write down the first 4 terms.....

    2. find the sum of the following geometric series

    50 + 40 + 32 + .......

    i worked out r = 0.8, but i don't know how to work out how many terms there are to find the sum...

    and finally...

    3. in a geometric series sequence Un, U2 = 4 and U4 = 16/9

    find the two possible values of its common ration r and first term a.

    Any help with any of these would be great..... thanks.
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    3. in a geometric series sequence Un, U2 = 4 and U4 = 16/9

    find the two possible values of its common ration r and first term a.

    Any help with any of these would be great..... thanks.[/QUOTE]

    aq=4
    aq3=16/9
    aq3/aq=16/9/4
    q(common difference)= +2/3,-2/3
    aq=4, a=4/q, a=6 or a= -6
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    2. find the sum of the following geometric series

    50 + 40 + 32 + .......

    I have forgotten the formula, but you have to do a sum to infinity
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    (Original post by ainat87)
    1.
    10
    ∑ 2r - 3
    r=1

    i have to write down the first 4 terms.
    -1, 1, 3, 5
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    (Original post by ainat87)
    I have a couple of questions that I'm stuck on, wondering if anyone can help....

    1.
    10
    ∑ 2r - 3
    r=1

    i have to write down the first 4 terms.....

    2. find the sum of the following geometric series

    50 + 40 + 32 + .......

    i worked out r = 0.8, but i don't know how to work out how many terms there are to find the sum...

    and finally...

    3. in a geometric series sequence Un, U2 = 4 and U4 = 16/9

    find the two possible values of its common ration r and first term a.

    Any help with any of these would be great..... thanks.
    2. if r<1 then sum to infinity =a/(1-r)=50/0.2=250
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    10
    ∑ 2r - 3
    r=1

    Doesn't the 10 above mean work to the first 10 terms?

    Anyway. put r equal to 1, 2, 3 and 4 to get:

    2*1-3, 2*2-3, 2*3-3, 2*4-3

    which is
    -1, 1, 3, 5
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    (Original post by mik1a)
    10
    ∑ 2r - 3
    r=1

    Doesn't the 10 above mean work to the first 10 terms?

    Anyway. put r equal to 1, 2, 3 and 4 to get:

    2*1-3, 2*2-3, 2*3-3, 2*4-3

    which is
    -1, 1, 3, 5
    no it means sum of all (2r-3), from when r=1 to r=10 which i suppose it wot u said..
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    wow. thanks you guys.
 
 
 

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