Protractor Practice: Build an Angle, Then Measure It

This example demonstrates an interactive workflow: students first construct an angle in the coordinate plane (by choosing rays/points and shaping the configuration), and then measure the constructed angle using a protractor tool to verify the result. The core concepts include the geometric definition of an angle, constructing angles via lines/segments and intersection points, and using angle-measuring tools (protractor-based measurement) to connect the visual construction with numerical angle values. Construction is carried out with GeoGebra commands such as Circle, Line, Intersect, Rotate, Angle, Segment, and Point; it also includes explicit protractor objects (e.g., protractor and protrac2) and angle/label displays. Typical objects include multiple points and angle notations (like α, β, γ, δ, ε, ζ, θ), along with auxiliary graphics (such as pic1/pic2 and measurement text). Suitable for middle and high school geometry lessons, classroom demonstrations, and student practice on angle measurement and geometric construction.