Geometric Proof of the Cosine Difference Formula

This GeoGebra example demonstrates a geometric proof of the cosine difference formula cos(α-β) = cos α cos β + sin α sin β. Using geometric constructions on the unit circle—including points, segments, angles, and orthogonal lines—it visually illustrates the derivation process. By constructing circles, intersections, reflections, and perpendicular lines, combined with the geometric relationships of