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Learning about
Circles
This page is printable
Finding
Circumference Practice Page
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Circle
Terminology
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Students should
be able to:
draw circles,
and identify and determine relationships among the radius,
diameter, center and circumference.
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Diameter
and Radius
- The diameter
is the distance across a circle through the center. You can
see what the diameter looks like by drawing a line through a
circle, making sure it goes through the point in the middle,
called the center.
- The radius
is the distance from the center to a point on the circle. The
radius is exactly half the length of the diameter.
Diameter and Radius
Mini-Movie
Click the button
on the left to draw the diameter. Click button on the
right to draw the radius. After it is drawn, it will move
to show that it is half the length of the diameter.
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Circumference
Circumference
is the perimeter of a circle, or the distance around the outside
the circle.
Circumference
Mini-Movie
Click the button
to make the red dot trace the circumference of the circle.
The radius and diameter are also shown so that you do
not confuse them with the circumference. |
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Formula
for finding the circumference of a circle
The circumference
of a circle is approximately 3.14 times the size of its
diameter. We know the number 3.14 as π,
or pi. So the formula for finding the circumference of
a circle is:
C = dπ
where d = diameter and C
= circumference
Since the diameter
of a circle is twice as long as the radius, we can also
use another formula:
C = 2πr
where r = radius and C =
circumference
Printable
- Finding Circumference Practice Page
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Tangent
A tangent is a straight line that
just touches a circle. In fact, it only touches the circle at
one point. The tangent line is perpendicular to the radius drawn
to this point.
Tangent
Mini-Movie
Click the button on the
left to see on line meet the circle at a point and form
a tangent. Click the button on the right to see another
one. |
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Everything
Geometry
The
Basics | Classifying
Quadrilaterals | Classifying
Triangles
Area
& Perimeter | Angles
| Circles
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