Vocabulary
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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
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A radius is exactly one-half of a diameter.
Therefore a diameter is twice a radius.
If the radius is 5.5 cm, then the diameter
is ___________
cm.
11
5.5 cm
Circumference
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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.
Homework Time