A Primer on Plotting

Plotting any algebraic expression is fairly straightforward in Sketchpad 3. Follow these steps:

  1. Create axes.
  2. Place a point on the x-axis and measure its coordinates.
  3. Use the calculator to isolate the x-coordinate of the point.
  4. Use the calculator to create an expression for y(x).
  5. Select the x-coordinate and shift-select the y(x) value.
  6. Choose Plot as (x, y) from the Graph menu.
  7. Select the plotted point and shift-select the x-point.
  8. Choose Locus from the Construct menu.
You should now have a plot of your expression. If the calculation is dependent on other geometric quantities, the plot will respond dynamically to changes in those quantities.

This technique assumes you want to plot Y as a function of X. You can obviously measure things differently and plot X as a function of Y. If you change the Grid to display a polar coordinate system (in the Graph:Grid Form menu), Plot as (x, y) becomes Plot as (r, theta), with which you can plot polar functions as well. Check out the sample Odds and Ends sketch which comes with Sketchpad 3 for ideas about plotting parametric functions.



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Sketches, scripts, and web pages by Bill Finzer and Nick Jackiw.