Sigma summation on TI Nspire CX (non-CAS)

[Joseph Martin]

Hi, I was wondering how to use the sigma function with a formula in TI-Nspire. Example:  (There is a little i [in terms of the variable, not the square root of -1] next to the 2 little n's in the numerator of both fractions, and i is an index that runs the sum a definite number of times, depending on its value.)

How would you enter this into the calculator? Any help is welcome, because I read a book and I still couldn't figure it out.

Thanks,

Joseph

[Dennis Donovan]

Joseph,

You want to think of it as a sum of a sequence.  If you know how to create the sequence, then you "wrap" a sum command around the sequence command.

For example: to get the sum of the first n integers -> sum(seq(k,k,1,n)) where you have to give n a definite value.

(I apologize for the screen shots, I just noticed that you put Non-CAS - but that only means that you would have to replace the n with an actual value.)

For your sum: on a CAS you could not use lower and upper case n's since the Nspire see's these both as the same variable (so I used k for small n, and n for capital N).

So assuming that you know the value of N in your summation, you would replace the n with that value.

The first screen shot shows the sum assuming that the n's are the first so many integers, the second screen shot shows the n's as a set of numbers as indexed into a list "num".

The third screen shot shows the use of the sigma template.

If this is not what you're looking for, then provide some context as to how you want to use this.  Because you're setting the sum equal to H' does that mean you're trying to define a function for example H'(x) = sum as i goes from 1 to x of your sequence?

Hope this helps.

Dennis Donovan

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From: Joseph Martin <j.jm...@gmail.com>
To: tins...@googlegroups.com
Sent: Sunday, March 31, 2013 1:42 AM
Subject: [tinspire] Sigma summation on TI Nspire CX (non-CAS)

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[Joseph Martin]

Dennis,

Thank you so much; this is exactly what I was asking for. I still haven't completely figured out how to use the sum() and seq() functions yet, but now I understand how to use the array and the sigma template in Nspire.