Question about Casio FX-300MS Calculator

# How to use log values in calculators - Casio FX-300MS Calculator

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You have two keys [LN] and [LOG], the former to calculate the natural logarithms and the latter to calculate the logarithms in base 10. You press the appropriate function key then type in the value. No need to press the [=] sign.
In case you are wondering: these functions have inverses: the inverse function of [LN] is the exponential, accessed with the key sequence [SHIFT][LN]; the inverse function of the logarithm in base 10 is "raise to to a power", accessed with the key sequence [SHIFT][LOG].
I am enclosing a screen capture from the user's manual. It shows you several examples.

Posted on Aug 24, 2010

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Posted on Jan 02, 2017

SOURCE: Using logs

log x base y = log x / log y
log (x*y) = log x + log y
log (x/y) = log x - log y

so log 24 base 2 it's log 24 / log 2 etc.
and if i get right what you wrote x= 10 ^ ( 3 * (log 5) ) if no inverse it it's easy really Hope it's helped you.

Posted on Jul 06, 2009

to calculate logb to base a,perform logb /loga

Posted on May 17, 2008

Like you maybe know in math (I know!) log x base y = log x / log y
so what you need its just input your number (x for example) and log it, than divide log x by log 2.
just: log x / log 2. (by the way in calculator the meaning of log x is log x base 10 the default base is 10)

Posted on Jul 06, 2009

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## Related Questions:

### Finding value of log with base 10

Use the "log" key. For example, to calculate the log base 10 of 2, press
"log" "2" =

Mar 29, 2012 | Casio FX991ES Scientific Calculator

### How to find pH

Do you have the concentration? if YES, you CALCULATE the pH with the relation
pH=-log(c) where c is the value of concentration in mol/L.
ex: c= 3.57x10^(-6)
pH: (-) [LOG] 3.57 [2nd][EE] [(-)] 6 [ ) ]
Here you have 2 change sign key press [(-)]

If you have the pH, and want to calculate the concentration that yields that value of the pH you proceed as follows
c= 10^(-pH)
Ex pH=8.23
c: [2nd][LOG] [(-) 8.23 [)]

Here is a screen capture to show you both calculations

Dec 05, 2011 | Texas Instruments TI-Nspire Graphic...

### How do i give the value of log

For common log, use the LOG key. For natural log, use the LN key. In either case, enter (or calculate) the value of the argument and then press the appropriate key.

To calculate the common log of 2, press 2 LOG =

To calculate the natural log of 2, press 2 LN =

Sep 08, 2011 | Texas Instruments TI-30XA Calculator

### When I go to use the 'log' button on TI 30XA I do not come up with the same answer as in my course book (for the examples) No real instructions on logs in the little instruction book. Have tried...

You calculate the pH with the relation
pH=-log(c) where c is the value of concentration in mol/L.
ex: c[H+]= 3.57x10^(-6)
pH: (-) [LOG] 3.57 [2nd][EE] [(-)] 6 [ ) ]
Here you have 2 change sign key press [(-)]

If you have the pH, and want to calculate the concentration that yields that value of the pH you proceed as follows
c= 10^(-pH)
Ex pH=8.23
c: [2nd][LOG] [(-) 8.23 [)]

General shortcut.
If concentration is of the form c[H+]= 1*10^(-a) where a is an integer between 0 and 14, the pH is equal to the positive value of exponent.

Ex:c[H+]=1x10^(-5) Mol/L then the pH is just the positive value of the exponent, ie 5 because pH=-log(1.x10^-5) =- log1 -log(10^-5)=0 -(-5)=5
Above I use the rule log(axb)=log(a)+log(b) , the rule log(a^b) = b*log(a)and the facts that log(1)=0 and log(10)=1, the last being true if log stands for log in base 10.

May 17, 2011 | Texas Instruments TI-30XA Calculator

### Conversion of log base 10 to log base 2

To calculate the log base 2 of a value, calculate its log and then divide by the log of 2. You can use either the log or the ln keys, but be consistent. For example, to calculate the log base 2 of 16, you can calculate either log(16)/log(2) or ln(16)/ln(2).

Nov 27, 2010 | Casio FX570MS Scientific Calculator

### How do I calculate pH from H+ concentration on a ti 30a? [H+] 1.2 x 10 -5 M = ? pH = 4.9 I worked out pH to concentration but struggling for the opposite figured it out once and...

You calculate the pH with the relation
pH=-log(c) where c is the value of concentration in mol/L.
ex: c[H+]= 3.57x10^(-6)
pH: (-) [LOG] 3.57 [2nd][EE] [(-)] 6 [ ) ]
Here you have 2 change sign key press [(-)]

If you have the pH, and want to calculate the concentration that yields that value of the pH you proceed as follows
c= 10^(-pH)
Ex pH=8.23
c: [2nd][LOG] [(-) 8.23 [)]

General shortcut.
If concentration is of the form c[H+]= 1*10^(-a) where a is an integer between 0 and 14, the pH is equal to the positive value of exponent.

Ex:c[H+]=1x10^(-5) Mol/L then the pH is just the positive value of the exponent, ie 5 because pH=-log(1.x10^-5) =- log1 -log(10^-5)=0 -(-5)=5
Above I use the rule log(axb)=log(a)+log(b) , the rule log(a^b) = b*log(a)and the facts that log(1)=0 and log(10)=1, the last being true if log stands for log in base 10.

May 20, 2010 | Texas Instruments TI-30XA Calculator

### Y=log x on calculator

the log of x is always 1 if your function reads y=log(x). if you insert a value for x, hit log, then enter the value, close the parentheses and hit enter for the value

May 01, 2010 | Texas Instruments TI-30 XIIS Calculator

### Some y values in my table say error when i graph logs

That is normal behavior. The log functions are not defined if the argument (x value ) is negative.

Mar 23, 2010 | Texas Instruments TI-83 Plus Calculator

### How to find pka value

Hello,
If I guessed right you are talking about the Chemistry notion of the pKa
Let the equilibrium constant be Ka =1.8x10^(-5). Then by definition pKa=-log(Ka) , log in base 10
pKa = - log(1.8x 10^(-5))
First set [MODE] to [COMP] by pressing [MODE] 1.
[LOG] [(] 1.8 [x] [SHIFT] [10 to the x] [(-)] 5 [)] . [(-)]
The [(-)] key is the change sign key : a small - between parentheses. The last [(-)] sign in the expression takes the negative of the whole calculation to obtain the correct value of the pKa.
The value you should find for the above exemple is 4.74

Hope it helps.

Dec 17, 2008 | Casio FX-115MS Plus Calculator

### How to calculate log value in calculator with different base value

In any scientific calculator log2(n) can be  calculated with either ln or log function as follows

Log2(n)= ln(n) / ln(2)

Or
Log2(n)=log(n) / log(2)

both will give nearly the same answers

Dec 08, 2007 | Casio FX-300MS Calculator

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