Constructing a Perpendicular Line Using GeoGebra

This example demonstrates how to construct a line that is perpendicular to a given line in the plane, producing a clear 90° relationship in the diagram. The key math ideas are geometric construction, the definition of perpendicular lines, and using known geometric objects (points and lines) to derive a new line with the required orientation. In GeoGebra, the construction is carried out using the command “Line” to create straight-line objects from the involved entities A, B, C, and a function/object f that supports the target or auxiliary geometric relationships. The activity is well suited for middle and high school geometry lessons, especially for practicing perpendicular/angle constructions, as well as for classroom demonstrations and self-study of geometric reasoning with dynamic geometry software.