Key Concepts: Secants, Tangents, and Angle Measures

Angles Formed by Secants and Tangents

• Two secants from an interior point: angle = ½(sum of intercepted arcs).
• Two secants from an exterior point: angle = ½(difference of intercepted arcs).
• Secant and tangent from an exterior point: angle = ½(difference of intercepted arcs).
• Two tangents from an exterior point: angle = ½(difference of intercepted arcs).
• Tangent and chord: angle = ½(intercepted arc).

Key Insight

For interior angles: use the sum of arcs. For exterior angles: use the difference of arcs.