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A.P.

by shashank.ism » Tue Feb 09, 2010 1:01 pm
If log 2, log (2x -1) and log (2x + 3) are in A.P., then x is equal to

5/2
log25
log32
3/2
1/2
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by sanjayviti » Tue Feb 16, 2010 3:32 am
shashank.ism wrote:If log 2, log (2x -1) and log (2x + 3) are in A.P., then x is equal to

5/2
log25
log32
3/2
1/2
Solve log(2x+3)- log(2x-1)=log(2x-1)-log2


(2x+3)/(2x-1)= (2x-1)/2

Get x=5/2
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by outreach » Tue Feb 16, 2010 7:23 am
do log problems appear in GMAT?
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by harsh.champ » Thu Feb 18, 2010 4:30 am
outreach wrote:do log problems appear in GMAT?
Well,I dont know in detail but this problem only uses basic log properties.
The questions that require changing of log bases,advanced log properties don't appear on the GMAT.
I guess just knowing basic log properties like addition,subtraction is enough.

Anyways,even if you forget the properties,it can be derived using "e".
I guess everyone knows the properties of the exponents and the log properties can be derived from there.

Ex:-Let log a = x
log b = y

Then,a = e^x
b= e^y

Now,a*b = (e^x)(e^y) = e^(x+y) [Using the properties of exponents]
Hence,log (ab) = x + y = log a + log b

Like this you can also prove the similar properties. :)
It takes time and effort to explain, so if my comment helped you please press Thanks button :)



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