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 May 22nd, 2016, 11:16 PM #1 Banned Camp   Joined: May 2016 From: earth Posts: 703 Thanks: 56 What is log function? Hello, Why we use log function in mathematics?
 May 22nd, 2016, 11:22 PM #2 Math Team   Joined: Nov 2014 From: Australia Posts: 688 Thanks: 243 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 $\displaystyle \int\dfrac{1}{x}\,dx = \ln |x| + C$. Thanks from MMath
 May 22nd, 2016, 11:47 PM #3 Banned Camp   Joined: May 2016 From: earth Posts: 703 Thanks: 56 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?
 May 23rd, 2016, 01:54 AM #4 Senior Member   Joined: Apr 2014 From: UK Posts: 883 Thanks: 323 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 01:55 AM. Reason: brackets went smiley on me
May 23rd, 2016, 02:11 AM   #5
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Quote:
 Originally Posted by MMath 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.

 May 23rd, 2016, 04:51 AM #6 Banned Camp   Joined: May 2016 From: earth Posts: 703 Thanks: 56 I have CASIO fx 82 ms please tell how to do this?
May 23rd, 2016, 04:55 AM   #7
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Quote:
 Originally Posted by MMath 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...

 May 23rd, 2016, 05:05 AM #8 Banned Camp   Joined: May 2016 From: earth Posts: 703 Thanks: 56 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??
May 23rd, 2016, 05:12 AM   #9
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Quote:
 Originally Posted by MMath 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.

 May 23rd, 2016, 05:23 AM #10 Banned Camp   Joined: May 2016 From: earth Posts: 703 Thanks: 56 i am not getting please tell in step.

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