math question - curves

[rivet]

I am trying to work out a formula for a curve, but am completely lost on how to get the equation.

x = 10 (time)

y = distance

y has to move to zero, and the curve is steep at the begging.

I have attached a jpg of the curve.

[cellmaker]

Rivet -

While it's not clear what you're trying to accomplish, there are many formulas to give you something like what you're showing.

Try (for x>0) y=1/x.

Cheers.

[rivet]

Charlie,

Thanks for the reply. I have attached a FMP file which might help.

I am trying to plot numbers from start to zero through

a number of step that will represent a curve.

I would like

curve.zip

[-Queue-]

y = 200/x for all x > 0

y will never touch 0, but will get infinitely closer.

[jrb12]

Rivet,

Unfortunately I don't have version 7 and the trial has expired so wasn't able to look at your attachment. But your curve could be generated using a displaced parabola. Consider the equation:

y = ( ( x - n ) ^ 2 ) / n

Where the ^ symbol represents 'to the power of' and

n is the number of steps.

So for n=10 the (x,y) pairs are:

(0 , 10) , (1 , 8.1) , (2 , 6.4) , ... , (8 , 0.4) , (9 , 0.1) , (10 , 0).

Cheers,

John.

[rivet]

Thanks guys, I am almost there... now can I have it so the 'y' starts at 200 and curves to 0 in ten steps?

[jrb12]

Rivet,

Change the parabola to:

y = ( ( x - n ) ^ 2 ) * a

where a is the factor of n^2 that gives the sarting value of y. So for n=10 (10 steps), at x=0 (the starting value of x), set a = 2 to make y = 200. I had assumed, god knows why, that you wanted the y (for x=0) to be the same as x (for y=0). Anyway, adjust the value of a accordingly to give whatever starting value for y you like.

Cheers,

John.

[rivet]

John, That did it... many thanks.

[cellmaker]

Sorry I dropped out of the thread - preoccupied. I'm glad to see that Math Club is alive and well on FMForums!

[rivet]

How about a reverse of the formula? Curve from 0 - n

[jrb12]

Rivet,

The reverse of your formula takes a little longer to work out ... eh eh ... no, I just dropped out of the forums for a while, as well.

To start y at zero, remove the displacement term to put the min value of the parabola back on the origin:

y = ( x ^ 2 ) * a

where a is the same as in the previous formula.

Cheers,

John.