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July 22nd, 2017, 06:11 PM   #1
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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 !
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July 22nd, 2017, 06:18 PM   #2
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depends on where you place the negative one ...
Attached Images
File Type: png log_(-1).png (1.6 KB, 11 views)
File Type: png log_(-1)_2.png (1.6 KB, 11 views)
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July 22nd, 2017, 06:21 PM   #3
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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 $\dfrac{1}{\log_a(x)}$.
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Last edited by skipjack; July 23rd, 2017 at 05:26 AM.
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July 22nd, 2017, 06:36 PM   #4
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Quote:
Originally Posted by skeeter View Post
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 06:41 PM.
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July 22nd, 2017, 06:47 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?
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July 22nd, 2017, 07:10 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?
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July 22nd, 2017, 07:14 PM   #7
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Quote:
Originally Posted by skeeter View Post
$50 \cdot \log^{-1}(-0.1)$ ...

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
File Type: jpg IMG_3324.jpg (19.3 KB, 6 views)
File Type: jpg IMG_3325.JPG (40.3 KB, 7 views)

Last edited by Angus; July 22nd, 2017 at 07:19 PM.
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July 22nd, 2017, 07:30 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
File Type: png inverse_log.png (1.0 KB, 10 views)
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July 23rd, 2017, 04:49 AM   #9
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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 !
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July 23rd, 2017, 05:07 AM   #10
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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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