Constructing Perpendicular Lines and Measuring the Right Angle

This example demonstrates how to construct a perpendicular line to a given line and how to verify the right-angle relationship using an angle measurement. The key math ideas include straight lines, orthogonality (perpendicularity), the foot of a perpendicular, intersection points, and using an angle object to visually confirm the perpendicular condition. In GeoGebra, you create the base lines with Line from point pairs (e.g., using objects A, B for line f and C, D for line g), then generate the perpendicular via OrthogonalLine from the chosen point relative to the target line. Next, Intersect is used to find the key crossing point of the constructed perpendicular with the original line, and Angle is used to define/display the angle (object α) that should be 90 degrees. Suitable for middle and high school geometry, as well as for instruction on geometric construction, right-angle verification, and perpendicular line concepts using dynamic mathematics software.