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How to write the ± (plus/minus character)?

Posted 10 years ago
Hi! I have to solve a limit, so i wrote:

lim (x^2+1)/(x+1) as x->±inf

but the ± is not being recognized, how can i write it?

Thank you for your time!
POSTED BY: Vincenzo Navarra
4 Replies
Many of Mathematica's characters have multiple ways of entering them, but a nice trick to remember is that the TeX code for the character with an escape before and after often works.

In this case, esc + \pm + esc does the trick
POSTED BY: Sjoerd de Vries
You have also
DirectedInfinity[1]
DirectedInfinity[-1]
DirectedInfinity[Cos[a] + I Sin[a]]

for a real variable a at your disposal.

Q: Is there also a DirectedInfinity[0]?
POSTED BY: Udo Krause
I'm using wolfram alpha, and ended up doing it 2 times, one for infinity, and one for -infinity. Thank you for your answer!
POSTED BY: Vincenzo Navarra
Hi, are you using Mathematica or Wolfram|Alpha?

It's possible to enter this symbol into Mathematica:[url=] reference.wolfram.com/mathematica/ref/PlusMinus.html
You can enter it into Mathematica by typing:
\[PlusMinus]
It is a symbol without any built-in meaning. You can define a meaning for it, but without it, Mathematica will not know what to do with it:
http://reference.wolfram.com/mathematica/tutorial/OperatorsWithoutBuiltInMeanings.html
I would evaluate the limit with both positive and negative infinity separately instead of defining the operator.

If you are looking to use Wolfram|Alpha, this has been asked once before here.
In short, you can't use Plus-Minus with Wolfram|Alpha. Enter each query individually:

lim (x^2+1)/(x+1) as x->infinity

lim (x^2+1)/(x+1) as x->-infinity
POSTED BY: Sean Clarke
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