Parameters (cursors)

Parameters or cursors are real values which can move in a fixed interval, e.g. between -5 and +5. The real value may be changed by moving a cursor with the mouse below the controls at the right of the geometrical representation. There are two kinds of parameters: formal and numeric parameters. Formal parameters have a formal name which is used in all exact calculations, and a numeric value which is used for all numeric evaluations (including graphical representation of objects depending on the parameter). They can therefore be used to make an analytical proof of a geometrical theorem using the CAS engine, while displaying a figure. Numerical parameters evaluate always to their numerical value, they can not be used to make an analytical proof (only to make conjectures like with most interactive geometry softwares).

To add a new parameter, use the Geo->Edit->Add parameter menu. For example, add a level with f(x):=a*x^2+b*x+c then define 3 parameters named a, b, c and add the command plot(f(x)), then move one of them to see the influence of each parameter on the shape of the parabola. You could also add a level mini:=solve(diff(f(x),x)) and M:=point(mini[0],f(mini[0])) to display the minimum. Note that the coordinates of M are displayed in terms of a and b under the commandline defining M at the left. You would have to add a level with evalf(coordonnees(M)) to see the current numerical value.