Tangent and its theorems

• If the line is tangent to a circle, then it is perpendicular (they form a 90-degree angle) to the radius drawn to the point of tangency.

  Theorem 1
• If the line is perpendicular to the radius of a circle at its endpoint that is on the circle, then the line is tangent to the circle.

  Theorem 2
• If two segments from the same exterior point are tangent to a circle then the two segments are congruent.

  Theorem 3
• It is a line that is tangent to two circles in the same plane.

  Common tangent
• The segment joining the center of the two circles.

  Common internal tangent
• Tangent that do not intersect the segment joining the center of two circles.

  Common central tangents