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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: 90,455

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.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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

ElainaVW
Member
Registered: 2013-04-29
Posts: 306

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: 3,564

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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