Presentation on theme: "Circles and Circumference Lesson 9-5. Vocabulary A circle is a plane figure that consists of a set of points that are equidistant from a given point called."— Presentation transcript:
Vocabulary A circle is a plane figure that consists of a set of points that are equidistant from a given point called the center. The circumference of a circle is the distance around it.
Identifying the Parts of a Circle A radius is a line segment that connects the outside of the circle to its center.
A diameter is a line segment with both endpoints on the circle that passes through the center.
A chord is a line segment whose endpoints are on the circle. Chords do not have to pass through the center of the circle. However, if a chord does pass through the center, it is also considered a diameter.
Numerical Relationships A radius is exactly one-half of a diameter. Therefore a diameter is twice a radius. 5.5 cm If the radius is 5.5 cm, then the diameter is ___________ cm. 11
Circumference Remember, circumference is the distance around the circle. If you divide a circle’s circumference by its diameter, you always get the same irrational number – pi (symbol: ¶ ) This is true of every circle. We estimate pi to be 3.14 or the fraction 22/7.