circles

• point of tangency


  a tangent intersects a circle only at one point
• circumscribed angle


  tangent segments that intersect outside of an circle and create an angle
• sectant-tangent product theorem


  $(AC)(BC)=$$(DC)^2$

  
• sectant-sectant product theorem


  $(AC)(BC)=$$(EC)(DC)$

  
• chord-chord product theorem


  $(AE)(EB)=$$(CE)(ED)$

  
• circle


  a collection of points that are equilateral from a central point
• radius


  only segment whose endpoints are the center of the circle
• diameter


  a circle whose segment whose midpoints are the center of the circle and endpoints lie on the circle
• chord


  only segment whose endpoints lie on the circle
• central angle


  angle whose vertex is on the center of the circle
• inscribed angle


  an angle whose vertex lies on the circle
• an arc


  portion of a circle
• intercepted arc


  an arc that is within the side of a central angle
• minor arc


  an arc whose measure is less than 180 degrees
• major arc 


  an arc whose measures is greater than 180 degrees
• tangent line 


  a line that intersects a circle only at one point
• sectant line


  a line that intersects a circle at two
• central angle theorem


  a central angle that has the same measure as its intercepted arc
• inscribed angle theorem


  a inscribed angle that is half the measure of its intercepted arc
• intersected quadrilateral


  a quadrilateral inside a circle where the vertices lie
• intersected quadrilateral theorem 


  $m<a+$$m<c=$$180$
• sectant-tangent interior angle


  m<1 = 1/2 (mAB)

  
• sectant-tangent exterior angle


  m<1 = 1/2 (mAB-mAC)

  
• sectant-sectant exterior angle


  m<1 = 1/2 (mAB-mDC)

  
• tangent-tangent exterior angle

  m<1 = 1/2 (mABC-mAC)

  
• intersecting chords angle


  m<1 = 1/2 (mAB+mCD)

  
• quadratic equation in standard form

  a$ax^2 +$$bx+$$c=$$0$
• circumference of a circle

  $2\pi r$
• length of an arc


  $\pi rx/180$
• median measure of a given angle

  $\pi rx/180$
• area of circle


  $\pi r^2$
• sector


  portion of a circle that is bounded by two radii and their intercepted arc
• area of sector


  $\pi r^2 (centralangle)/180$