Math Is Fun Forum
  Discussion about math, puzzles, games and fun.   Useful symbols: √ ∞ ≠ ≤ ≥ ≈ ⇒ ∈ Δ θ ∴ ∑ ∫ π -

Login

Username

Password

Not registered yet?

#1 2013-05-13 14:19:50

Dyoni
Novice

Offline

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)+log(3).(5)
then.. log(3)+log(3)+log(5)+log(3)+log(5)
and that's all equal to.. x+x+y+(x+y) = 2x+y+(x+y) = 2x√x+y√y

but the real answer is (5x+2y)

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

Thank's..

Last edited by Dyoni (2013-05-13 14:20:35)

#2 2013-05-13 14:31:07

bobbym
Administrator

Offline

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 have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

#3 2013-05-13 15:37:13

ElainaVW
Full Member

Offline

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 (2013-05-13 15:48:30)

#4 2013-05-14 13:15:51

John E. Franklin
Star Member

Offline

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

Board footer

Powered by FluxBB