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# Limes (lim, limit) sometimes only works with fractions, not with decimals.

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HP Prime

As you can see in the picture below, if you use a decimal number as limit (here 2.5) then the result will be undefined.

This is confusing. Because for the last operation with 1/x, decimal numbers are obviously working (2.1)

Is there a good reason for this behavious?

Would it make sense, that the HP-Team would implement to use the exact() function behind the lim for the x->value?

Thanks.

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Doing something like converting input always to "exact" while mostly good behavior, could definititely be detrimental in other cases.

The general rule simply remains, while in the CAS avoid doing any approximations until any final step in an operation. That matches pretty well with what I was explained back in my school days from pretty much any professor too... 🙂

To quickly do this yourself, tap the history item once in the CAS (so the limit is selcted) and then press A B/C key. That throws "exact" around your expression for further evaluation.

TW

Although I work for the HP calculator group as a head developer of the HP Prime, the views and opinions I post here are my own.
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Thank you so much for this proposal to use the A B/C key.

This is a very good solution!!!

Please add this hint to the HP-Prime Manual in the Limit section.

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It is described in the a b/c key and CAS sections I beleive already...

Glad you like it. That is why I designed it that way.

TW

Although I work for the HP calculator group as a head developer of the HP Prime, the views and opinions I post here are my own.
† The opinions expressed above are the personal opinions of the authors, not of HP. By using this site, you accept the Terms of Use and Rules of Participation