How do I use 'k' or 'n' instead of 'x' on my TI-89?

In summary: No, there is a difference. 'N' and 'k' represent whole numbers, while 'x' represents real numbers. When you use 'x', you're implicitly using the real number system. However, you can also explicitly use the real number system by using (-1)^(k+1).
  • #1
lazycritic
15
0
Hi,

I'm trying to figure out my TI-89. So I want to estimate the 40th partial sum of this series:

Sum(40) of (-1^(k+1))/k^4, starting at k=1. My major problem is that I want to use 'k's or 'n's, not 'x's. Is there a difference? I haven't asked my Calc teacher about this yet, but I know that 'k's and 'n's deal with integers while 'x's encompass the real numbers.

When I do the sum with 'x', I get a a number -1.08232 but the book shows .094703.

I hate the way that all these manuals show n and k, and presume you can input those variables -- but I haven't seen an 'n' or 'k' variable, and when I use the capital letters it doesn't work.
 
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  • #2
lazycritic said:
Hi,

I'm trying to figure out my TI-89. So I want to estimate the 40th partial sum of this series:

Sum(40) of (-1^(k+1))/k^4, starting at k=1. My major problem is that I want to use 'k's or 'n's, not 'x's. Is there a difference? I haven't asked my Calc teacher about this yet, but I know that 'k's and 'n's deal with integers while 'x's encompass the real numbers.

When I do the sum with 'x', I get a a number -1.08232 but the book shows .094703.

I hate the way that all these manuals show n and k, and presume you can input those variables -- but I haven't seen an 'n' or 'k' variable, and when I use the capital letters it doesn't work.

The 'n' and 'k' are typically called 'indices.' In mathematics, the convention is that 'n' and 'k' are often used to represent whole numbers, and 'x' often represents real numbers. Generally, to a calculator, 'n' and 'x' are just variables. It may be that 'x' is indeed dedicated to real values; perhaps there is a corresponding "delta" x which regulates the increments of the value 'x'. For example, when graphing, the "delta" x determines how far apart each point is plotted before "connecting the dots."

Also, check the syntax for the sum() command to see if you're using it properly. And be careful (esp. with TIs) when using -1^(k+1); to be safe, I'd write this as (-1)^(k+1).
 
  • #3
So if I use x when all these instructions tell me to use 'n' or 'k', it shouldn't matter?
 

What is a sequence and how can it be represented on a TI-89 calculator?

A sequence is a set of numbers that follow a specific pattern or rule. On a TI-89 calculator, sequences can be represented using the Sequence Editor, which allows you to enter the first term of the sequence, the rule for generating the sequence, and the number of terms to display.

How can I find the sum of a sequence using a TI-89 calculator?

To find the sum of a sequence on a TI-89 calculator, you can use the Sum function. This function allows you to enter the first term, the rule for generating the sequence, and the number of terms to be added. The calculator will then calculate the sum of the sequence and display the result.

Can the TI-89 calculator handle infinite sequences and sums?

No, the TI-89 calculator is not capable of handling infinite sequences and sums. It has a limit of 999 terms for sequences and sums.

How can I graph a sequence on a TI-89 calculator?

To graph a sequence on a TI-89 calculator, you can use the SeqGraph function. This function allows you to enter the first term, the rule for generating the sequence, and the number of terms to be graphed. The calculator will then plot the points and connect them to show the graph of the sequence.

Are there any shortcuts or tips for working with sequences and sums on a TI-89 calculator?

One helpful tip for working with sequences and sums on a TI-89 calculator is to use the arrow keys to scroll through the terms of a sequence or sum. You can also use the "n/d" key to quickly enter the number of terms for a sequence or sum. Additionally, using the "sum" key will allow you to quickly find the sum of a sequence without having to enter the terms manually.

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