# TI-89 returns the series I entered

• Apr 15th 2011, 03:47 PM
Wolvenmoon
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.
• Apr 15th 2011, 05:44 PM
topsquark
Quote:

Originally Posted by Wolvenmoon
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
• Apr 16th 2011, 12:19 AM
mr fantastic
Quote:

Originally Posted by Wolvenmoon
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&#40;ln&#40;x&#41;&#47;x,x,2,infinity&#41 ; - Wolfram|Alpha

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