Autograph Forums

Hi all,

I was wondering if there is a way to model volumes by shells with Auotgraph?

All the best,
Libman

Hi libman,

"Kindof" is the best answer I can give you.  In Autograph you can either do a volume of revolution of the area under y = f(x) around y = k where you specify k OR you can do a volume of revolution about any straight line.  In the latter case the volume is not calculated.  

So to show a volume by shells (but not calculate it):

1. Plot y = f(x)
2. Select your curve > right-click > Find Area to find the area between two points
3. Plot x = 0
4. Select Slow Plot
5. Select the area and the line x = 0
6. Right-click > Find Volume...

Hope this helps,

Simon

Works perfectly as a visual tool! Would be great to see the volumes values - BUT, fantastic as far as I am concerned. I can teach the theory much more easily with the 3D plot.

Might be best to clarify that a person needs to be working in 3D mode and also understand how to rotate a region about the x axis or a line parallel to the x axis first.

To all: See http://www.autograph-maths.com/inaction/td/Volumes.htm

Miss communicating with you SImon.

Thanks,
Libman,
aka G.Landry

I need to find the volume for y=f(x) rotated about x=0...how do I do that please?  Also, we do not have the Plot as 2D function in the 3D window when we want to plot the y=f(x).  Please advise

Many thanks

Dear slake60,

First of all you need to check whether the version of Autograph you have is new enough to support Volumes of Revolution. Go to Help > About, you need Version 3.2 or above.

If you have the a recent version then to rotate about x = 0 do the following:

1. Enter an equation y = f(x)
2. Select "Plot as 2D equation" and click OK
3. Select the curve, right-click Find Area.
4. Enter an equation x = 0.
5. Select the area and the line x = 0, right-click and select Volume.

Hope that helps,

Simon