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Math Help - TI84 PLUS SUMMATION sequence

  1. #1
    Member helloying's Avatar
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    TI84 PLUS SUMMATION sequence

    My cal has OS2.53

    A seq of no.  X_1,X_2... is such that x_1=1 and x_{n+1}=\frac{5}{X_n} +1

    Find the value of N such that \displaystyle\sum_{n=1}^N X_n is less than 60
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  2. #2
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    earboth's Avatar
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    Quote Originally Posted by helloying View Post
    My cal has OS2.53

    A seq of no.  X_1,X_2... is such that x_1=1 and x_{n+1}=\frac{5}{X_n} +1

    Find the value of N such that \displaystyle\sum_{n=1}^N X_n is less than 60
    1. I assume that you are looking for the greatest number N such that the sum is less than 60. Right?

    2. I didn't find a way to do the necessary calculations in one step, but I had to use 2 steps:

    3. Switch the calculator into SEQ-mode.
    4. Enter at y=

    nMin=1
    u(n)=5/(u(n-1))+1

    (You'll find the u at 2ND 7)

    5. Go to TBLSET

    TblStart = 1
    \DeltaTbl = 1

    6. Create the sequence and store it into the list L1:

    seq(u(n),n,1,21,1) STO L1

    7. Next step

    sum(L1)

    8. To change the limits of the summation you can recall the last commands by using 2ND ENTER
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