. The line tool is the farthest right. Since it doesn't matter where the line is, just click and drag to create the two points that define the line. Then construct two additional points on the line. First off, we're going to need a coordinate grid. Go to Graph -> Grid Form -> Square Grid. You can use rectangular here if you want, the only difference is you have the option of differing scales with a rectangular grid. Once you have your grid, create a line, using the line tool.
If you click and hold on the line segment tool you get this sub-menu: . The line tool is the farthest right. Since it doesn't matter where the line is, just click and drag to create the two points that define the line. Then construct two additional points on the line.
Now we need to create a line segment for the changes in y and x. Highlight one of the constructed points and an axis. With both selected, go to construct -> perpendicular line. Select the other constructed point and the other axis and construct another perpendicular line. Select both lines and construct an intersection point. Using the constructed points will allow us to change their position while maintaining the initial direction of the line.
Now for a few cosmetic changes. Select both lines and then go to Display -> Hide (ctrl-h). Now you'll have a floating point (so to speak) so you'll need to construct a couple of line segments to that point.
Next we're going to discuss Δy and Δx. We can't use distance, since we will be looking for some negative values. We'll have to do this by coordinates. Select a point and measure the abscissa and the ordinate. Do this for every point.
Next we're going to calculate the slope. Go to Measure -> Calculate and the calculator dialog will appear. Click on the appropriate measurement boxes on the GSP screen and they'll appear in the calculator window. When you're done with the calculation click OK and it will appear on the GSP window.
What you have now is a dynamic drawing that can show that the slope is constant on a line.
