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    What is the sum of n terms of the following series:

    a) x + 1 + 1/x + ...

    b) 1 - y + y^2 - ...
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    (Original post by Abbie_D)
    What is the sum of n terms of the following series:

    a) x + 1 + 1/x + ...

    b) 1 - y + y^2 - ...
    find the common ratio and use the summation formula
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    (Original post by TeeEm)
    find the common ratio and use the summation formula
    Thanks for the reply. I have done but I still cannot get the exact answers. :confused:
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    (Original post by Abbie_D)
    Thanks for the reply. I have done but I still cannot get the exact answers. :confused:
    post your working and I will try to point you in the right direction
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    (Original post by TeeEm)
    post your working and I will try to point you in the right direction
    The answer is x^n-1/x^n-2(x-1)

    My working so far:

    Sn = x[(1/x)^n-1]/1/x-1
    = x^n-1/1/x-1


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    (Original post by Abbie_D)
    The answer is x^n-1/x^n-2(x-1)

    My working so far:

    Sn = x[(1/x)^n-1]/1/x-1
    = x^n-1/1/x-1


    first line is fine

    What is the answer meant to be, because the expression will be ugly no matter what
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    Answer is: xn - 1 / xn-2(x-1)
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    (Original post by Abbie_D)
    Answer is: xn - 1 / xn-2(x-1)
    can you see how to get your answer to that
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    (Original post by TeeEm)
    can you see how to get your answer to that
    No, sorry :confused:
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    (Original post by Abbie_D)
    No, sorry :confused:
    expand the bracket at the top
    then multiply top and bottom by xn
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    (Original post by TeeEm)
    expand the bracket at the top
    then multiply top and bottom by xn+1
    I'm still puzzled. Would it be possible if you could show your working to me please?
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    (Original post by Abbie_D)
    I'm still puzzled. Would it be possible if you could show your working to me please?
    [x(1/xn - 1)]/[1/x-1]


    =[1/xn-1 - x]/[1/x-1]

    multiply to and bottom by xn-1
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    (Original post by TeeEm)
    [x(1/xn - 1)]/[1/x-1]


    =[1/xn-1 - x]/[1/x-1]

    multiply to and bottom by xn-1
    I can understand up to: 1 - (x1 x xn-1 ) / xn-1 (1/x - 1)n
    And I know how to get xn - 1 on the top, but how do you get the xn-2
    (x-1) on the bottom?

    I really appreciate your help by the way!
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    (Original post by Abbie_D)
    I can understand up to: 1 - (x1 x xn-1 ) / xn-1 (1/x - 1)n
    And I know how to get xn - 1 on the top, but how do you get the xn-2
    (x-1) on the bottom?

    I really appreciate your help by the way!
    the bottom should look

    1/xn-1[1/x-1]


    =1/xn-1 1/x[1 - x]

    =1/xn-2[1 - x]
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    (Original post by TeeEm)
    the bottom should look

    1/xn-1[1/x-1]


    =1/xn-1 1/x[1 - x]

    =1/xn-2[1 - x]
    Thank you so much
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    (Original post by Abbie_D)
    Thank you so much
    my pleasure
 
 
 
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