velohead66

Need some help re-arranging a formula.
I'm sure I used to be able to do them easily, but it's been sooooooo long.

I need to re-arrange.......
Y = X * R^N
......to N =

I get to ...
Y/X = R^N
but cant get any further

Is there some trick to swopping R^N to something like N^R

tathan

it's possibly

N= log˅R(Y/X)

which is

N=log˅R(Y) - log˅R(X)


Worrying how **** my maths has become really.

Gregsti01

iTrader: (1)

Y/X=R to the power of N would it not give you y/x squared to the power of R =N ?

LostUser

I think this is correct

http://oakroadsystems.com/math/loglaws.htm

AndyC_772

iTrader: (2)

Y = X * R^N

Y/X = R^N

log (Y/X) = log (R^N)

log Y - log X = log (R^N)

log Y - log X = N log R

N = (log Y - log X) / log R

RobJenks

Andy you are correct - Come on down !

Leslie

There must be more to life than that!

Les

AndyC_772

iTrader: (2)

<hangs head>

I'm an engineer....

dunx

iTrader: (3)

I perspire to be one, but that's plain mathematics...

dunx

P.S. Tired and hungry, didn't help !

Alg

I'm genuinely in awe of that.
Could you give me an example where it could be put to a practical use, just so I can convince myself I should've paid more attention at school.
I haven't got a clue what that all relates to.

AndyC_772

iTrader: (2)

Much as I hate to say it, the most useful thing I've ever got out of this sort of academic work is qualifications that look good on my CV. Without them it's hard to get a job in science, engineering or other technical areas, even if you never actually use those skills once you've got the job.

I probably spend no more than 10-20% of my time at work actually doing 'serious' development. The rest is spent dealing with suppliers, producing documentation, building prototypes and other stuff that doesn't need any great technical skill. But I'd never have got the job without a degree.

Sometimes that stuff really is useful, of course, and some people will use it every day. (Maybe the OP could give us a clue as to what that particular equation describes?)

One example I do use is the equation which models how a capacitor charges and discharges. Capacitors are used in electronics to remove unwanted electrical noise, provide time delays so things can happen at defined speeds, to isolate different parts of a circuit while allowing signals to pass between them, and numerous other uses. One governing equation is: Vc = V0 (1 - e^(-t/RC)), and it's solved using logarithms.

Leslie

I was joking really, I could not remember how to do it anyway!

Les

Alg

Nope, still no good.

Thanks for taking time to answer though.

velohead66

Most obscure maths is relevant to some real life application, but most of what we learn in school NEVER gets used. Certainly in my case.
But, quite often, stuff i did donkeys years ago comes up once in a while.



The original equation relates to growth (of say a financial asset).
y = x * (1+r)^n

where....
y = sale price
x = purchase price
n = number of periods (eg 10 for 10 years)
r = growth rate

so, if you buy a house for x, sell for y, and held for 10 years, then r is your growth.


But of course my algerbra is somewhat diminished these days.

I thought the answer was something to do with log, but even that area of maths has all evapourated from my brain over the years too, as the last time I used a log was at least 15 years ago. D'oh!

Thanks for the answer(s) though, do appreciate it, guys.