My Math Forum Log with negative exponent on TI-84 Plus Calculator

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 July 22nd, 2017, 05:11 PM #1 Newbie   Joined: Jul 2017 From: Meridian, ID Posts: 7 Thanks: 0 Log with negative exponent on TI-84 Plus Calculator Good evening to all - I have what may be a very basic (Newbie) sort of question ... I have a TI-84 Plus calculator, and I don't understand how to enter a log raised to the -1 power, on the calculator keypad ... An example of the formula I need to solve on the calculator is: 50 x Log-1(-0.1) Note that the "Log-1" is actually supposed to be Log raised to the -1 power (Not sure how to make the -1 appear as an exponent of the word Log - lol) Thanks in advance, for any suggestions !
July 22nd, 2017, 05:18 PM   #2
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depends on where you place the negative one ...
Attached Images
 log_(-1).png (1.6 KB, 11 views) log_(-1)_2.png (1.6 KB, 11 views)

 July 22nd, 2017, 05:21 PM #3 Senior Member   Joined: May 2016 From: USA Posts: 1,150 Thanks: 479 I know nothing about your calculator, but if what you want to compute is $\log_a \left ( x^{-1} \right )$ you can do so with $-\log_a(x)$. If what you want to compute is $\{\log_a(x)\}^{-1}$ you can do so with $\dfrac{1}{\log_a(x)}$. Thanks from Angus Last edited by skipjack; July 23rd, 2017 at 04:26 AM.
July 22nd, 2017, 05:36 PM   #4
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Quote:
 Originally Posted by skeeter depends on where you place the negative one ...
Yes, that's the problem it is actually written as the word Log with the -1 exponent immediately after the word Log .... So it is Log to the -1 power ... and that is then multiplied by another number (I wish I could paste an image of the formula on here, so you could see it).

*** Just like this formula, except that the -1 is an exponent (Log raised to the -1 power): log-1(x+3)

Last edited by Angus; July 22nd, 2017 at 05:41 PM.

July 22nd, 2017, 05:47 PM   #5
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Quote:
 50 x Log-1(-0.1)
$50 \cdot \log^{-1}(-0.1)$ ...

note this will yield an imaginary result ... you sure the $0.1$ in parentheses is negative?

July 22nd, 2017, 06:10 PM   #6
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Quote:
 (Log raised to the -1 power): log-1(x+3)
$\log^{-1}(x+3) = \dfrac{1}{\log(x+3)}$

now ... what are you trying to make the calculator do?

July 22nd, 2017, 06:14 PM   #7
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Quote:
 Originally Posted by skeeter $50 \cdot \log^{-1}(-0.1)$ ... note this will yield an imaginary result ... you sure the $0.1$ in parentheses is negative?
log4(x+3)-
Here is an image of the formula - http://mymathforum.com/attachment.ph...1&d=1500775993

Thanks Skeeter - I think we are getting close to a solution to my dilemma. I attached images so you can see the entire formula - Yes the 0.1 is actually negative. As mentioned, the only thing I'm struggling with is how to enter the Log raised to the -1 power, on the calculator keys.
Attached Images
 IMG_3324.jpg (19.3 KB, 6 views) IMG_3325.JPG (40.3 KB, 7 views)

Last edited by Angus; July 22nd, 2017 at 06:19 PM.

July 22nd, 2017, 06:30 PM   #8
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your text is using $\log^{-1}(-0.1)$ as an inverse log notation, that is ...

$\log^{-1}(-0.1) = 10^{-0.1} = 0.7943...$
Attached Images
 inverse_log.png (1.0 KB, 10 views)

 July 23rd, 2017, 03:49 AM #9 Newbie   Joined: Jul 2017 From: Meridian, ID Posts: 7 Thanks: 0 Thanks Skeeter (and others who helped). I have rarely ever worked with Logs, and did not understand that this was an inverse Log function. I think I can do these problems now - Thanks again for the kind assistance !
 July 23rd, 2017, 04:07 AM #10 Math Team   Joined: Jul 2011 From: Texas Posts: 2,771 Thanks: 1426 fyi, inverse log used to be written antilog(whatever) in the old days of log tables. To be honest, it's been a while since I've seen the negative one inverse notation used with logarithms ... kind of rare, actually.

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