Drawing tangents at 10 points

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Patts - 27 Nov 2003 00:48 GMT

Hello, How can you draw tangents at 10 different points
in excel. I am using Office 2000. As the gradient at each
tangent, will give me the velocity at that time.

regards
spatts265@yahoo.co.uk

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David J. Braden - 27 Nov 2003 06:41 GMT

Do you know the function of the curve? If y9ou can, differentiate it, or
take a central difference: at point x where you want the gradient, use
(f(x+d)-f(x-d))/(2*d), for "small" positive d.
If these don't do the trick, look in this NG a few days back for a similarly
titled post, and responses.

HTH
Dave Braden
.

> Hello, How can you draw tangents at 10 different points
> in excel. I am using Office 2000. As the gradient at each
> tangent, will give me the velocity at that time.
>
> regards
> spatts265@yahoo.co.uk

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- 27 Nov 2003 23:48 GMT

Hello, I tried using the polynomial line which goes
through the points of degree 2. But the equation given is
y = -2E-06x2 + 0.0023x + 0.236 which I dont understand.
If I use the method of linest, I am left with y=mx + b, I
can diff but I will not be able to get velocity at each
point as the x would be eliminated once diff.

To be more precise, I have a set of x values which is the
height from 100cm to 190cm. The y values are the time it
takes for the object to fall, in sec.

any other suggestions

regards

>-----Original Message-----
>Do you know the function of the curve? If y9ou can, differentiate it, or
[quoted text clipped - 14 lines]
>
>.

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Tushar Mehta - 30 Nov 2003 13:41 GMT

In line.

> Hello, I tried using the polynomial line which goes
> through the points of degree 2. But the equation given is
> y = -2E-06x2 + 0.0023x + 0.236 which I dont understand.

What do you not understand? I'd hazard a guess that the coefficient of
x^2 is not significant. Also, to improve on the rounding, double click
the equation and adjust the number of decimal values.

> If I use the method of linest, I am left with y=mx + b, I
> can diff but I will not be able to get velocity at each
> point as the x would be eliminated once diff.

LINEST, contrary to the documentation, works with non-linear equations.
For one example see Bernard Liengme's
http://www.stfx.ca/people/bliengme/ExcelTips/Polynomial.htm

> To be more precise, I have a set of x values which is the
> height from 100cm to 190cm. The y values are the time it
> takes for the object to fall, in sec.

Huh? You are plotting t=f(s), not s=f(t), where s is distance and t is
time. Since the equation of distance as a function of time is
s=1/2*constant-acceleration*t^2 + initial-speed*t + initial distance,
in your case the result is s=1/2*g*t^2, where g is the acceleration due
to gravity. So, t=Sqrt(2s/g).

> any other suggestions
>
> regards

Signature

Regards,

Tushar Mehta, MS MVP -- Excel
www.tushar-mehta.com
Excel, PowerPoint, and VBA add-ins, tutorials
Custom MS Office productivity solutions

> Hello, I tried using the polynomial line which goes
> through the points of degree 2. But the equation given is
[quoted text clipped - 36 lines]
> >
> >.

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