page_title: Tangent lines to circles
section_title: Inner tangent
hierarchical_section_title: Tangent lines to circles / Tangent lines to two circles / Inner tangent
context_page_description: In Euclidean plane geometry, a tangent line to a circle is a line that touches the circle at exactly one point, never entering the circle's interior. Tangent lines to circles form the subject of several theorems, and play an important role in many geometrical constructions and proofs. Since the tangent line to a circle at a point P is perpendicular to the radius to that point, theorems involving tangent lines often involve radial lines and orthogonal circles.
context_section_description: An inner tangent is a tangent that intersects the segment joining two circles' centers. Note that the inner tangent will not be defined for cases when the two circles overlap.
caption: Inner tangent. The external tangent lines pass through the internal homothetic center.