Summation Notation for TI86

Date: 10/29/2001 at 21:59:46
From: Nicole Colt
Subject: Summation notation for TI86

Dear Dr. Math,

I am currently taking Calculus 1 from the community college in town.  
We were talking about summation notation and I was wondering if there 
was an easier way to do our assignment on a TI86. We are allowed to 
use a program called MatLab, but I am usually unable to get the lab 
over before it closes down.

An example problem is:

    20
    sigma (2^k)/k
     k=1
 
Thank you for your help, 
Nicole Colt

Date: 10/29/2001 at 23:20:02
From: Doctor Paul
Subject: Re: Summation notation for TI86

What you want to do is create a sequence and then sum the sequence.  
Both menu items are contained under the "List > OPS" (2nd + 
subtraction key, then F5) category.

For example if you wanted to compute:

   4
 sigma   k^2
 k = 1

You would do:

seq(x^2,x,1,4)  

[you can't use k as the variable - it will cause a syntax error]

and the Calculator would return the list:

{1 4 9 16}

Then to sum the values:

sum Ans

and the calculator gives the answer: 30.

Or you could do it all in one step:

sum seq(x^2,x,1,4)

and you get 30.

So for your problem you would do:

sum seq( 2^x/x,x,1,20)

The answer is:  

111142.374448 = 1617069867008/14549535

[The calculator wouldn't tell me how to write the given number as a 
rational number - I used a different computer program to do that.]

I hope this helps. Write back if you'd like to ask some more questions 
about it.

- Doctor Paul, The Math Forum
  http://mathforum.org/dr.math/