Circle Theorem 5: Radius to a Tangent

① This example demonstrates the circle theorem that the radius drawn to the point of tangency is perpendicular to the tangent line. ② Core mathematical concepts include circles, tangents, radii, perpendicular relationships, and angle measurement. ③ Construction highlights: a Circle command creates circle c; Point commands define center A and tangency point B; Segment connects A and B to form radius a; Tangent draws the tangent line b at B; Angle measures the angle γ between the radius and the tangent; auxiliary objects such as point C and segment d are also used. ④ Suitable for middle‑school geometry lessons, high‑school review, and as a dynamic GeoGebra tutorial for beginners.