GeoGebra 3D Beginner Tutorial: Exercise 1
NEW TOOLS WE WILL LEARN HOW TO USE:
Move 
Point 
Plane Through 3 Points 
Intersect Two Surfaces 
In this introductory exercise, we'll learn a means through which students can discover the intersection of any 2 (non-parallel) planes.
Point
Plane Through 3 Points
Intersect Two Surfaces
In this introductory exercise, we'll learn a means through which students can discover the intersection of any 2 (non-parallel) planes. DIRECTIONS:
1) Select the POINT tool. Use this tool to plot 3 points anywhere on the gray plane.
2) Select the MOVE arrow. Click twice on any one of the points you plotted in step (1).Use this tool to
move this point off of the gray plane. Repeat this process for the other 2 points.
3) Select the PLANE THROUGH 3 POINTS tool. With this tool highlighted, select the 3 points you
initially plotted in step (1). This will create a plane that passes through these 3 points.
Note: This step could have also been done without plotting the points first (step 1).
Steps (1) - (2) were included here simply to acquaint you with plotting & moving points in 3D.
Further directions appear below this applet.
tool. Use this tool to plot 3 points anywhere on the gray plane.
2) Select the MOVE arrow. Click twice on any one of the points you plotted in step (1).Use this tool to
move this point off of the gray plane. Repeat this process for the other 2 points.
3) Select the PLANE THROUGH 3 POINTS tool. With this tool highlighted, select the 3 points you
initially plotted in step (1). This will create a plane that passes through these 3 points.
Note: This step could have also been done without plotting the points first (step 1).
Steps (1) - (2) were included here simply to acquaint you with plotting & moving points in 3D.
Further directions appear below this applet. 4) Select the MOVE 
arrow. Use this tool to drag any one (or more) of these 3 points around. Notice
how the plane you plotted in (3) always passes through these 3 points.
5) Now select the INTERSECT 2 SURFACES 
tool. Select the plane you plotted in step (3). Then select
the gray plane. This will now plot the intersection of these 2 surfaces (here, planes).
arrow. Use this tool to drag any one (or more) of these 3 points around. Notice
how the plane you plotted in (3) always passes through these 3 points.
5) Now select the INTERSECT 2 SURFACES tool. Select the plane you plotted in step (3). Then select
the gray plane. This will now plot the intersection of these 2 surfaces (here, planes). QUESTION:
What can we conclude about the intersection of any 2 non-parallel planes?
When you're done (or if you're unsure of something), feel free to check by watching the quick silent screencast below the applet.