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log0.5(19)+log2(19)=0

how to explain this?

 Jan 6, 2015

Best Answer 

 #2
avatar+130477 
+10

Here's a slightly different approach to Melody's

Note that we can write .5  as 1/2  = 2-1 

So we have

log2(19)  + log0.5 (19)   .....and...using the"change of base" rule, we can write

log(19) / log(2)  +  log(19) / log(.05) =

log(19) / log(2)  + log(19) / log(1/2) =

log(19) / log(2)  +  log(19) / log2-1 =

log(19) / log(2)  +  log(19) / (-1) log2 =

log(19) / log(2)  +  [ (-1) log(19) /  log2 ] = 

log(19) / log(2)  -  log(19) /  log2 =   0

 

 

 Jan 7, 2015
 #1
avatar+118703 
+5

Mmm interesting.

Let 

 

x=log0.5(19)andy=log2(19)so19=0.5xand19=2y19=(12)x2x=119so2x×2y=119×192x×2y=12x×2y=202x+y=20$therefore$x+y=0solog0.5(19)+log2(19)=0

 Jan 7, 2015
 #2
avatar+130477 
+10
Best Answer

Here's a slightly different approach to Melody's

Note that we can write .5  as 1/2  = 2-1 

So we have

log2(19)  + log0.5 (19)   .....and...using the"change of base" rule, we can write

log(19) / log(2)  +  log(19) / log(.05) =

log(19) / log(2)  + log(19) / log(1/2) =

log(19) / log(2)  +  log(19) / log2-1 =

log(19) / log(2)  +  log(19) / (-1) log2 =

log(19) / log(2)  +  [ (-1) log(19) /  log2 ] = 

log(19) / log(2)  -  log(19) /  log2 =   0

 

 

CPhill Jan 7, 2015
 #3
avatar+118703 
0

Thanks Chris 

It is always good to get a couple of different takes  

 Jan 7, 2015

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