angles and tangents

• The point of intersection of the line and the circle 


  point of tangency
• A line that is tangent to two circles in the same plane


  common tangent
• Do not intersects the segments joining the centers of the two circle.


  common external tangents
• An angle whose vertex is at the center of the circle.

  central angle
• An angle whose vertex is on the circle and whose sides contain chords of the circle.

  inscribed angle