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Q: Mathematics - Equation of a line ( No Answer,   1 Comment )
Question  
Subject: Mathematics - Equation of a line
Category: Reference, Education and News
Asked by: jamesb4210-ga
List Price: $5.00
Posted: 21 Jul 2004 21:11 PDT
Expires: 22 Jul 2004 17:18 PDT
Question ID: 377446
I want the equation of a line with a logarithmic curve, x-minimum 1
and x-maximum 30, y-minimum 1 and y-maximum 30,000.
Answer  
There is no answer at this time.

Comments  
Subject: Re: Mathematics - Equation of a line
From: d_albert77-ga on 22 Jul 2004 07:23 PDT
 
approximately, i believe, the equation should be:

1.41^x+ln(x)=y

This equation starts at (0,1),
and at x= 30 it is about 29,963.

If your really determined to get it to equal exactly 30,000, then play
with the 1.41  and change it to

n^30=29,998.533

and you get

n = 1.4100569946559586271749047307593

So, the more exact equation would be

1.4100569946559586271749047307593^x+ln(x)=y

which has points (0,1)

and

(30,30000.010121254719662437295027903)

which is pretty close to 30,000

Finally,


if you want to be even more exact then change the 1.41 for:

n^30=30,000-log(30)

This should theoritically give you the exact answer.

After some though, it might be easier to just change the 1.41 for the
n you get from n^30=30,000-log(30), without simplifing the n:

My ability for solving for bases is not as good as it used to be, but
I think you would get something like

n=10^(log(30,000-log(30)))/30

So the equivelent final answers withought decimals should be

10^(log(30,000-log(30)))/30^x+ln(x)=y

or more simply:
n^x+ln(x)=y

where n=10^(log(30,000-log(30)))/30

I got his by using log base 10, for some reason i couldnt do it using
(ln), which I though would not make any difference.

bassically i used the "properties of logs"
mainly the 3rd found in http://www.purplemath.com/modules/logrules.htm

which allowed me to move the exponent down.

A final note, this looks a lot more like a parapolic curve then a
logorithimic curve, used "graph" in google, and used an online
graphing calculator.

I argue though that both things are the same parabolic (almost=too) logorithmic,

if you really want the logorithmic feel though, you could always just
invert it by, starting at (30, 30,000), and just inversing the
equation.

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