1.2a Define an Angle with Points and Rays

This example demonstrates how to define and visualize an angle in plane geometry using three points and two rays. Core mathematical concepts covered include the definition of an angle, vertex, sides represented by rays, the interior of an angle, and standard angle notation. Construction highlights: based on the construction summary, the GeoGebra Ray command is applied to point objects A, B, and C to construct rays a and b, with text object text1 and auxiliary objects d, c, e, f used for labeling and visualization. Suitable for middle school geometry instruction, teacher classroom demonstrations, and student independent exploration of angle concepts and properties.