circles and circumference lesson 9-5. vocabulary a circle is a plane figure that consists of a set...
TRANSCRIPT
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 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.
Circumference Formulas
C = ¶dC = 2¶r
Example
41 m
C = ¶dC = (3.14)(41)
C = 128.74 m
We substitute 3.14 in for pi.
Homework Time