Formula for a curve?

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Hello. I would like to forst say that I am not sure what kind of math this falls under, so that is why I am posting it here. I also want to point out that I am really bad at math, but I have tried my best at finding a solution to this to no avail.

Here is what I have...

1=1, 25=6, 50=21, 75=45, 100=78

I will use a = 1-100 and b = 1-78 to help me understand and explain.

What I am trying to find is the formula so I can find "b" for any number between 1 and 100. I know it's a curve, and that if I was to use a straight line the solution WAS

a*.78=b

This however doesn't hold true for, say 50. 50 would equal 39 in this case and I need it to equal 21.

Any help would be VERY appreciated! Thank you so much in advance.

Bazil
 
I'm sorry, but I can't follow your post. If you could, please, reply with the complete text and instructions for this exercise.

Thank you.

Eliz.
 
As this is a personal project and not an exercise perhaps I am posting in the wrong forums. I am sorry. If I am not posting in error, then I will try to explain a bit better.

I am looking for the forumla for a curve. On a grid, I know a total of four points. I know (1,1) (25,6) (50,21) (75,45) and (100,78)

I am seeking the formula to give me the "y" coord when I know the "x" I could determine the straight line between each point, but I know there must be a smooth curve between (1,1) and (100,78) that will connect to each point.

My apologies,

Bazil
 
Gee Bazil, that's quite different from your 1st post.
I thought you were dealing with a series at first;
now I see (I think) you're dealing with an elliptical curve!
If, as you say, you're "really bad at math", why are you attempting this?
I presume the way to go is somehow develop an equation for this curve;
probably (I'll guess) by making right triangles using consecutive points:
like using (1,1) and (26,6) will give a right triangle with legs = 5 and 24.

But I'm not sure how you'd wrap that up: I'll let Stapel (who I know is
eagerly awaiting the chance to show you how) do that 8-)
 
There are infinitely-many curves that could be put through these points. The "formula" for such a process will depend on the type of curve you are wanting, and will likely be so complicated that it would be better to use regression software.

If you need your curve to pass through these exact points, then you could also use a polynomial.

What techniques do you know for curve-fitting?

Eliz.

P.S. This is a tutoring forum, so any tutoring question is appropriate. Since this forum doesn't a "statistics" category, regressions would best fit here in "other math". So post what you've got and what you've tried, and we'll try to help you work your way toward an answer.
 
Denis said:
I presume the way to go is somehow develop an equation...by making right triangles using consecutive points...I'll let Stapel...do that....
Click to expand...
I'm sorry, but I'm not familiar with your regression method. You'll have to provide the explanation and/or links.

Thank you.

Eliz.
 
I have been chalenged with making a program, and part of this program needs to have this curve to display a different, but proportional number to the user (1-100) but only use numbers from 1-78. It's difficult to explain this. Also, I am not as bad at math as I auusme I am, I would not have made it this far if I was. What I lack in knowledge, though, I make up in determination.

Part of this determination has spuulied me with this flawed forumla...

y=((x*x)/(130))+1

this is "fairly" accurate up to 1 unit, examples are:

(1*1)/130))+1=1
(25*25)/130))+1=5.80
(50*50)/130))+1=20.23
(75*75)/130))+1=44.26
(100*100)/130))+1=77.92

Is this as accurate as I could get? I am not sure.. My brain hurts.
 
Don't know, Baz. Your formula would be bang on for those points using the ceiling function:
y=ceiling[((x*x)/(130))+1]
 
Well, I must apologize for swearing at your set of points at first!

There is some sort of logic to them; if you start with (0,0) instead of (1,1), then:
0 to 6: 6/25
6 to 21: 15/25
21 to 45: 24/25
45 to 78: 33/25
Those are the gradual increases per unit of 0-25,25-50,50-75, 75-100.
You can see that the numerators constantly increase by 9....
Perhaps I need another coffee :idea:
 
Thank you

Thank you both, I have the answer now thanks to a little soundboarding and the suggestion of the ceiling command. Back to the PHP scripting for me.

Thank you again,

Bazil
 
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