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## #1 2013-05-12 16:19:50

Dyoni
Member
Registered: 2013-05-12
Posts: 1

### solving algorithm problem

Hi,
I have a probelm with this:
if log(3)= x and log(5)= y, then log(45√15) =...??

I tried this: log(45)+log(√15) = log(3).(3).(5)+½log(3).(5)
then.. log(3)+log(3)+log(5)+½log(3)+log(5)
and that's all equal to.. x+x+y+½(x+y) = 2x+y+½(x+y) = 2x√x+y√y

but the real answer is ½(5x+2y)

anyone can help me? please..I really confuse...

Thank's..

Last edited by Dyoni (2013-05-12 16:20:35)

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## #2 2013-05-12 16:31:07

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: solving algorithm problem

Hi;

Please check your "real answer," because when an answer does not agree with what I get it is almost certainly wrong. Okay, that is an exaggeration, it has a darn good chance of being wrong. Okay, that is stretching it too but check it anyway.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #3 2013-05-12 17:37:13

ElainaVW
Member
Registered: 2013-04-29
Posts: 580

### Re: solving algorithm problem

Try wolfram to check that.

Enter "PowerExpand[log(45 sqrt(15))]" the substitutions will verify Bobby's answer.

Last edited by ElainaVW (2013-05-12 17:48:30)

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## #4 2013-05-13 15:15:51

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,588

### Re: solving algorithm problem

the half thing seems right because log(400) is about 2.6 and 2.6/2=1.3 and log (20) sorta is 1.301, so that's good...

igloo myrtilles fourmis

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