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Negative log how do i perform negative log calculations? For example, -log(3.0x10^-2)

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Use the log function (common logarithm). See screen capture for markings on key.
negative log - 83c0b62.jpg
To evaluate the negative of a logarithm
Enter the number (argument) of the logarithm
Press the = key to have it calculated.
While result is still displayed, press the sign change key or (+/-).

Beware that -log(number) is not necessarily a negative value.

Another way to calculate -log is to use the relation
log(1/a)=-log(a) .

Your example

3 [EXP] [(] [+/-] 2 [) ] [LOG][=] [+/-]

[EXP] is the key to enter exponent of a power of 10 :It is a shortcut, so no 10 is entered. Respect the key sequence above.
[ (] left parenthesis to prevent ambiguity due to the negaticve exponent. Just a security.
[)] is the enclosing right parenthesis
[+/-] is the Sign Change key

Posted on Jun 22, 2010

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1 Answer

Negative log


You can do 0-log(number) or you can calculate the log value then negate it by pressing the change sign key marked (-) or +/- or (+/-).

Sep 06, 2012 | Texas Instruments TI-34II Explorer Plus...

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How to fix error mesage on TI-30Xa. Every time I press LOG an error sign comes up. how do i fix this?


To take the log of a number, enter the number then press the LOG button, then the =. To take the log of a negative number, enter the negative number using the +/- key just to the right of the decimal point. To calculate the negative of a log, calculate the log and then negate it using +/-. To calculate the antilog (inverse logarithm), press 2nd then LOG.

Bear in mind that LOG is the common (base-10) logarithm. For the natural (base-e) logarithm, use the LN key to its right.

Nov 07, 2011 | Texas Instruments TI-30XA Calculator

1 Answer

How to take anti log in casio fx 991 ms and give example?


Depending on the actual log function you are talking about, the inverse function (what you call the anti log) can be one of several things.
The inverse of the natural log (LN) is the exponential function e^x.
If y= ln(x) then x=e^y
On a calculator functions that are inverse of one another share the same physical key. If one function is marked on a key, the inverse function is usually the SHIFTED (or 2nd) key
The inverse of the common (decimal logarithm) is the power function with 10 as base.
Example: if y= log(x) then x=10^y
For an arbitrary base (must be positive) if y= log_b(x) then x=b^y.
Note: I do not think that the FX-300ms can perform log calculations in bases other than e (natural log) or 10 (common decimal log).

Aug 13, 2011 | Casio FX-300MS Calculator

1 Answer

Cannot calculate antilog value for negative numbers . Example: antilog(-5)


Make sure you use the (-) key to enter negative values, not the - key. For example, to calculate the common antilog of -5, press
SHIFT log (-) 5 =

To calculate the natural antilog of -5, press
SHIFT ln (-) 5 =

Apr 30, 2011 | Casio FX-115ES Scientific Calculator

1 Answer

I am having issues performing a simple function on my TI-30XS calculator. when I square a negative number - I get a negative number as opposed to a positive number?? example -3 - which I specify the...


You're not calculating the square of a negative number, you're calculating the negative of a square. You need to use parenthesis to indicate the square of a negative number.

You're calculating -(3^2), not (-3)^2.

To calculate the latter: ( (-) 3 ) x^2 =

Dec 05, 2010 | Texas Instruments TI-30XA Calculator

1 Answer

TI-84 Plus Silver Edition. When dividing negative powers of ten by other negative powers of 10 the calculator it just adds the the negative powers together. How do i fix this? An example: 5*10^-10 /...


To enter an exponent, positive or negative, use the EE (Enter Exponent) key (the shifted function of the , key just above the 7 key). Do 5 2ND [EE] (-) 1 0 / 5 2ND [EE] (-) 1 0 ENTER and you'll see 1.

What I think you're doing (I can't be sure without seeing your keystrokes) is calculating
5*10^-10/5*10^-10 which is interpreted as (5*10^-10/5)*10^-10, which indeed is 10^-20.

Oct 16, 2010 | Texas Instruments TI-84 Plus Silver...

1 Answer

How do you input -log ?


Use the log function (common logarithm). See screen capture for markings on key.
83c0b62.jpg
To evaluate the negative of a logarithm
Enter the number (argument) of the logarithm
Press the = key to have it calculated.
While result is still displayed, press the sign change key or (+/-).

Beware that -log(number) is not necessarily a negative value.

Another way to calculate -log is to use the relation
log(1/a)=-log(a) .

Jun 01, 2010 | Casio FX-260 Calculator

1 Answer

What button do I use to find negative log on my TI-83 calculator...also how do I put in a negative exponent?? i.e 1*10 to the negative 6th .....


You compute the negative of a logarithm the same way you compute the negative of anything else. However, do you really mean the antilog (inverse logarithm)? Use 2ND [e^x] for the natural antilog, 2ND [10^x] for the common antilog.

For negative exponents, as well as negative anything, use the (-) key next to the decimal point. For your example, 1 EE (-) 6

Feb 25, 2010 | Texas Instruments TI-30XA Calculator

1 Answer

How do i enter pH on a TI 30 calculator


Hello,
This post answers two questions
  1. How to obtain the concentration knowing the pH?
  2. How to obtain the pH knowing the concentration
If you are not interested in the theory, jump to the examples at the end of the post.

As you well know the pH is the negative of the log in base 10 of the H+/H3O+ ion concentration. If we use [H+] to represent that concentration, then pH=-log[H+].
To obtain the [H+] you need to calculate the antilog. You write the definition in the form log[H+] =-pH and then calculate 10 to the power of each member. The equality remains valid as both members are treated similarly. Thus
10^( log[H+] ) = 10^(-pH)
Since raising 10 to a power is the inverse function of taking the log in base 10, 10^(log(x))=log(10^(x)) = x (they are inverse of one another), you are left with

[H+]=10^(-pH)

Your calculator has a function [10 to x] accessed by pressing the [2nd] function key. To use it you must enter the negative value of the pH, press the [2nd] function key then the [10 to x], then the = key to get the result (concentration)
Examples

1. Let the pH=5.5, what is the H+ concentration?

With [(-)] being the change sign key, then
[H+]:[ (-) ] 5.5 [2nd][10 to x] [=]
The result is 0.000003162 or 3.16 x 10^(-6)

Calculating the pH

Shortcut:
For all H+/H3O+ concentrations of the form 1.*10^(a) where a is an integer number between 0 and -14, the pH is the negative value of the exponent.
Concentration =10^(-3), pH=3
Concentration=10^(-11), pH=11

For other concentrations such as 3.567*10^(-8), one cannot use the shortcut above, but have to calculate the log of the concentration

[H+/H3O+] = 3.567*10^(-8)
pH= - log(3.567*10^(-8))
This is keyed in as follows (to minimize the number of parentheses)

8 (-) [2nd][10 to x] [*] 3.567 [LOG] [=] (-)
Here you have two (-) change sign, the first is entered after the exponent of 10, the other at the end of the calculation to take the negative of the displayed result. You may notice that it is entered in the reverse order of the defining relation - log(3.567*10^(-8)).
To verify your calculation, the result is 7.447696891 or just 7.45
If you have a problem with the first (-) try entering it before you type in 8.


Hope it helps and thank you for using FixYa
And please, show your appreciation by rating the solution.

Dec 07, 2009 | Texas Instruments TI-30XA Calculator

6 Answers

How do i use the inverse log operation on the TI-84


The problem is simple. You're trying to get an [H+] concentration which is obviously going to have a value of some number times ten raised to a negative power. Therefore, you have to insert the negative value of the pH into the 10^(x). When you insert said negative number you will come out with the right answer.
i.e.
The pH of a sample of human blood was calculated to be 7.41. What is the [H+] concentration of the blood?
10^(-7.41) = [H+]
[H+] = 3.9 E-8  
(the answer should only have two sig. figs because the pH has two digits after the decimal.

Jun 10, 2008 | Texas Instruments TI-84 Plus Calculator

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