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Math Help - TI-89 returns the series I entered

  1. #1
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    TI-89 returns the series I entered

    Hi,

    I'm trying to get my TI-89 to do a series for me. The series is from n to infinity of ln(x)/x. When I put that in, it's spitting out what I put in.

    What am I doing wrong? Exactly entered as summation(ln(x)/x,x,2,infinity)

    Edit: I know it diverges by the integral test. I'm using my TI-89 as a check and I've had this problem with convergent series before until I modified my index, but it's getting to be a nuisance.
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  2. #2
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    Quote Originally Posted by Wolvenmoon View Post
    Hi,

    I'm trying to get my TI-89 to do a series for me. The series is from n to infinity of ln(x)/x. When I put that in, it's spitting out what I put in.

    What am I doing wrong? Exactly entered as summation(ln(x)/x,x,2,infinity)

    Edit: I know it diverges by the integral test. I'm using my TI-89 as a check and I've had this problem with convergent series before until I modified my index, but it's getting to be a nuisance.
    My TI-92 does the same thing. My guess is that since the sum cannot be calcuated in closed form it only gets to the point of knowing the summation is undetermined. It'd be nice if it said that, though.

    -Dan
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  3. #3
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    Quote Originally Posted by Wolvenmoon View Post
    Hi,

    I'm trying to get my TI-89 to do a series for me. The series is from n to infinity of ln(x)/x. When I put that in, it's spitting out what I put in.

    What am I doing wrong? Exactly entered as summation(ln(x)/x,x,2,infinity)

    Edit: I know it diverges by the integral test. I'm using my TI-89 as a check and I've had this problem with convergent series before until I modified my index, but it's getting to be a nuisance.
    summation(ln(x)/x,x,2,infinity&#41 ; - Wolfram|Alpha

    The problem with CAS calculators is that they are misnamed. They should be called Wannabe-CAS calculators.
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