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May 23rd, 2016, 12:16 AM   #1
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What is log function?

Hello,
Why we use log function in mathematics?
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May 23rd, 2016, 12:22 AM   #2
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The log function was developed to transform multiplication problems into simple addition problems.

Suppose that $a$ and $b$ are horrible-looking decimals and we want to work out $ab$. If we take the logarithm of this, we get $\log (ab) = \log a + \log b$ by a simple law of logarithms.


There are other reasons, such as the useful fact that $\displaystyle \int\dfrac{1}{x}\,dx = \ln |x| + C$.
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May 23rd, 2016, 12:47 AM   #3
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PLEASE GIVE EXAMPLE MORE:

a=5.7895
b=2.2358

a*b=? = 12.9441
log(ab)=log a +log b
=0.76264 + 0.34943=0.26649
they are not same?
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May 23rd, 2016, 02:54 AM   #4
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a=5.7895
b=2.2358

a*b= 12.9441
log(ab)=log a +log b
log(12.94416) = log (5.7895) + log (2.2358 )
1.112074 = 0.762641 + 0.349433
They are the same.

Last edited by weirddave; May 23rd, 2016 at 02:55 AM. Reason: brackets went smiley on me
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May 23rd, 2016, 03:11 AM   #5
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Quote:
Originally Posted by MMath View Post
PLEASE GIVE EXAMPLE MORE:

a=5.7895
b=2.2358

a*b=? = 12.9441
log(ab)=log a +log b
=0.76264 + 0.34943=0.26649
they are not same?
Remember that $ab = e^{\ln (ab)}$, so it's not quite as simple as that.
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May 23rd, 2016, 05:51 AM   #6
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I have CASIO fx 82 ms please tell how to do this?
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May 23rd, 2016, 05:55 AM   #7
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Quote:
Originally Posted by MMath View Post
I have CASIO fx 82 ms please tell how to do this?
I have fx-3650P and fx-50H. In both, the ln button is below x^3. Perhaps this is also true of your model...
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May 23rd, 2016, 06:05 AM   #8
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Nothing is coming i have taken example of a=5 and b=3 also..
log(a*b) = log5 + log 3 = 0.698 + 0.477=1.175
so, e and e^x are coming in my calculator both are not giving 15??
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May 23rd, 2016, 06:12 AM   #9
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Originally Posted by MMath View Post
Nothing is coming i have taken example of a=5 and b=3 also..
log(a*b) = log5 + log 3 = 0.698 + 0.477=1.175
so, e and e^x are coming in my calculator both are not giving 15??
Use the ln button. The log button in Casio calculators is the common logarithm, not the natural logarithm.
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May 23rd, 2016, 06:23 AM   #10
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i am not getting please tell in step.
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