Stage 18 · Circles

18.5.2 The Test for a Tangent: Perpendicular Means Tangent

18.5 Tangent Lines — The Line That Only Kisses Once

Point 2 of 5

18.5.2 The Test for a Tangent: Perpendicular Means Tangent

Core idea

Turn it around — draw a line through the outer end of a radius at a right angle to it, and that line is guaranteed to be a tangent.

Module goal. Dig deep into the borderline case of tangency, mastering a tangent's properties, its test, and the tangent-length theorem, then apply them to a triangle's inscribed circle.

eastmath.com · 18.5 Tangent Lines — The Line That Only Kisses Once · 18.5.2 The Test for a Tangent: Perpendicular Means Tangent