EXPERIMENT WITH PARALLEL AND PERPENDICULAR
Background
GeoGebra has tool for easily constructing parallel lines and perpendicular lines. In this activity you will use these tools to experiment with parallel and perpendicular.
Step 1. The GeoGebra Parallel Line Tool
Now select the PARALLEL LINE tool 
. Read the instructions for this tool: SELECT POINT AND PARALLEL LINE. So, before you can use this tool, you need a point and line.
First make the line. Use the LINE tool 
to create a line anywhere on the GeoGebra page. This line is Line AB.
GeoGebra now needs to know how far away from this line to draw the new parallel line. Use the NEW POINT tool 
to create a Point C somewhere near the Line AB.
Now select the PARALLEL LINE tool. Click on Point C and then click anywhere on Line AB. You have constructed a new line that is parallel to Line AB at Point C.
Step 2. The GeoGebra Parallel Line Tool
Select the PERPENDICULAR LINE tool 
. Read the instructions for this tool: SELECT POINT AND PERPENDICULAR LINE.
You already have points and lines on the page, so use those to test this tool.
Click on Point C and then click on Line AB. The newly constructed line is perpendicular to Line AB at Point C.
Step 3. Experiment
Use the MOVE tool 
to grab and drag Point A, B, or C. Observe the three lines
as you do this. What do you notice?
Once you have constructed parallel or perpendicular lines in GeoGebra using these tools, they remain parallel or perpendicular even if you change their positions on the page.
. Read the instructions for this tool: SELECT POINT AND PARALLEL LINE. So, before you can use this tool, you need a point and line.
First make the line. Use the LINE tool to create a line anywhere on the GeoGebra page. This line is Line AB.
GeoGebra now needs to know how far away from this line to draw the new parallel line. Use the NEW POINT tool to create a Point C somewhere near the Line AB.
Now select the PARALLEL LINE tool. Click on Point C and then click anywhere on Line AB. You have constructed a new line that is parallel to Line AB at Point C.
Step 2. The GeoGebra Parallel Line Tool
Select the PERPENDICULAR LINE tool . Read the instructions for this tool: SELECT POINT AND PERPENDICULAR LINE.
You already have points and lines on the page, so use those to test this tool.
Click on Point C and then click on Line AB. The newly constructed line is perpendicular to Line AB at Point C.
Step 3. Experiment
Use the MOVE tool to grab and drag Point A, B, or C. Observe the three lines
as you do this. What do you notice?
Once you have constructed parallel or perpendicular lines in GeoGebra using these tools, they remain parallel or perpendicular even if you change their positions on the page.