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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
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,366

Re: solving algorithm problem

Hi;

Which does not agree with your real answer...

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.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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

ElainaVW
Member
Registered: 2013-04-29
Posts: 291

Re: solving algorithm problem

Try wolfram to check that.

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

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: 3,562

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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