Circles and Circumference Section 10.1 Geometry 2015-2016

Terms Circle – set of all ordered points that are equidistant from a given point (center), in a plane. Chord – segment whose endpoints are points on the circle. Radius – segment with endpoints that are the center and a point of the circle. Diameter – a chord that passes through the center of the circle.

Identify Parts of a Circle Name the circle Circle A Name a radius Name 2 chords Name a diameter

Important Theorems/Formulas All radii in a circle are congruent. A diameter (d) is composed of 2 radii (r). So all diameters in a circle are congruent. d = 2r

Find measures in intersecting circles The diameters of Circle A, Circle B, and Circle C are 10 inches, 20 inches, and 14 inches respectively. Find XB. d = 10 in circle A, AX = 5 d = 20 in circle B AB = 10 and BC = 10 AX + XB = AB 5 + XB = 10 XB = 5 Find BY d = 14 in circle C, YC = 7 BY + YC = BC BY + 7 = 10 BY = 3

What is Circumference? Circumference – is the distance around the circle. Circumference is represented by C The ratio of the circumference of a circle and the diameter of the circle is an irrational number called pi. (The Greek letter is used as the exact value.) If given the diameter: C = If given the radius: C =

Example Problems: Find C if r = 13 inches. C = Find C if d = 6 mm Find d and r if C = d = 34 If d = 34 then r = 17