Investigating Circles

Parts of the Circle: Radius – segment that goes from the center of the circle to a point on the outside of the circle. PR is a radius of circle P R P

It cuts the circle in half. QS is a diameter of circle P Diameter – a segment that goes from one point on the outside of the circle, through the center, to another point on the outside of the circle. It cuts the circle in half. QS is a diameter of circle P Q R P S

Chord – a segment with both endpoints on the outside of the circle. **A diameter is also a chord** LM, QS, and OT are all chords of circle P. M Q R P L O S T

QPR, RPS, and QPS are all central angles of circle P. Central Angle – An angle that has the center of the circle as its vertex. QPR, RPS, and QPS are all central angles of circle P. M Q R P L O S T

Identify the following: 1 diameter 2 radii 3 chords 3 central angles Answers: MD SD, SF, SM LN, MD, BG MSD, DSF, MSF B N L S M D F G

Finding Radius and Diameter The diameter is twice as big as the radius d = 2r r = d ÷ 2 Find the unknown length: r = 3 cm 2) d = 24 in d = ____ r = ____ (6 cm) (12 in) d = 35 m 4) r = 9.2 mm r = _____ d = ____ (17.5 m) (18.4 mm)