Acc. 10.4.notebook
April 08, 2013
DO NOW
1. Find the area of a parallelogram with base 12 inches
and height 3 inches.
2. The height of a trapezoid is 7 meters. The bases are
16 meters and 20 meters. Find the area of the trapezoid.
3. The area of a trapezoid is 132 square feet. The bases
are 30 feet and 36 feet. Find the height of the
trapezoid.
Mar 27­5:48 PM
10.4 Circumference and Area of a Circle
A circle consists of all points in a plane that are the same
distance from a fixed point called the center. The distance
between the center and any point on the circle is the radius.
The distance across the circle through the center is the
diameter.
The circumference of a circle is the distance around the circle.
Mar 27­8:25 PM
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Acc. 10.4.notebook
April 08, 2013
central angle
chord
arc
semicircle
For any circle, the ratio of its circumference to its diameter
is an irrational number that is approximately equal to 3.14 or
22. The Greek letter (pi) is used to approximate this ratio.
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Mar 27­8:30 PM
The diameter of a circle is 5
centimeters. What is the radius?
Find the circumference of the
circle. Round your answer to
the nearest whole number.
Mar 27­8:35 PM
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Acc. 10.4.notebook
April 08, 2013
The circumference of a circle is 22 meters.
Find the radius of the circle to the nearest
tenth of a meter.
Mar 27­8:39 PM
The circumference of a circle is 70 inches.
Find the radius of the circle to the nearest
inch.
Mar 27­8:40 PM
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Acc. 10.4.notebook
April 08, 2013
The diameter of a circle is 38
feet. Find the circumference of
the circle to the nearest foot.
When the radius of
a circle is divisible
by 7, use 22/7 to
approximate .
Otherwise, use 3.14
to approximate .
The circumference of a circle is 500 feet. Find the
radius of the circle to the nearest foot.
Mar 27­8:42 PM
Find the area of the circle to the nearest square foot.
What do we need to do first?
Mar 27­8:44 PM
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Acc. 10.4.notebook
April 08, 2013
The diameter of a circle is 54 inches. Find the area
of the circle to the nearest square inch.
Remember that area is measured in square units. The area
formula involves r2 and the circumference formula does not.
This should help you remember which is the area formula and
which is the circumference formula.
Mar 27­8:47 PM
The area of a circle is 250 square inches. Find the
radius of the circle to the nearest inch.
Mar 27­8:51 PM
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Acc. 10.4.notebook
April 08, 2013
Finding the area of a figure.
A Norman window from Congress Hall in
Philadelphia consists of a rectangle and
a half circle, as shown. Find the area of
the window to the nearest square foot.
Find the area of the rectangle.
Find the area of the half circle.
Mar 27­8:53 PM
What information do you need to know in
order to find either the area or the
circumference of a circle?
Mar 27­9:07 PM
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