PERPENDICULAR LINES
Instructions
When two lines intersect forming a right (90 degree) angle, geometers label that angle using a square so that it is clear that it is a special angle, a right angle. See the diagram below.
Use the MOVE tool 
to move the Drag Points of the two intersecting lines.
Try to orient the lines so that there is a right angle at their intersection.
Now drag the lines again and try to find other combinations that form a right angle at the intersection.
Once you have formed a right angle at the intersection of the two lines, what do you notice about all four of the angles formed?
When two intersecting lines or line segments form a right angle, the two lines or line segments are said to be perpendicular.
to move the Drag Points of the two intersecting lines.
Try to orient the lines so that there is a right angle at their intersection.
Now drag the lines again and try to find other combinations that form a right angle at the intersection.
Once you have formed a right angle at the intersection of the two lines, what do you notice about all four of the angles formed?
When two intersecting lines or line segments form a right angle, the two lines or line segments are said to be perpendicular.