A right triangle has one right angle. To construct a right triangle, you must construct two of its sides to be perpendicular. (Perpendicular segments intersect at a 90° angle.) If you construct a triangle to be right, then no matter how hard you try to stretch and change it by pulling on one of its vertices, it will always stay right.
Draw a right triangle made of three line segments. "Eyeball" two of the line segments so that it looks like they meet at a 90° angle.
Construct a right triangle. Notice that it would be difficult to tell which one was "drawn" and which one was "constructed" just by looking at your triangles.
Grab each of the vertices of the first triangle, one at a time, and drag them around. What changes? What stays the same?
Grab each of the vertices of the second triangle, one at a time, and drag them around. What changes? What stays the same?
To construct a perpendicular line, tell the computer what you want it to be perpendicular to and where you want it drawn. You need to select a segment (or a ray or a line) and a point before "Perpendicular Line" will be an option for construction. The software only constructs perpendicular lines, but you can create a segment on top of that line, then hide (don't delete!) the line. (Select the line, then choose "Hide Line" under the Display menu.) Close Tip
The Geometer's Sketchpad ® 2001, Key Curriculum Press, Emeryville CA, 1-800-995-MATH