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13 Perimeter and Area of a Circle
Basic Concepts The Perimeter and Area of a Circle
(Perimeter of a Circle) (Diameter)x(Pi)
(Area of a Circle) (Radius) (Radius) (Pi)
Pi is the ratio of the circumference of a circle to its diameter. Pi is a number,
approximately 3.14, and is usually represented by the Greek letter .
The figure below is made up of a circle and a polygon. To find the
perimeter of the colored part in the square, first, separate the parts with
straight edges from the parts with curved edges. Use the circumference of
a circle to find the lengths of the curved edges and the total perimeter. In
order to find the area of the colored part, add and subtract the areas of
different parts to obtain the shape of the known area.
Perimeter of the +++= +
Colored Part
Area of the +- =
Colored Part
Example Find the perimeter and the area of the colored 5 cm
part. 5 cm
Class Notes
The total length of the line segments of the colored part is equal to the perimeter of a
square that has sides of cm. The total length of the curved parts is equal to
the perimeter of a circle that has a radius of cm.
Therefore, the perimeter of the colored part is 4 3.14 cm.
When you add the area of the colored parts, the sum is equal to the area of a circle
that has a radius of 5 cm, therefore, 3.14 cm2.
112 NUMINO Challenge D1
Basic Concepts The Perimeter and Area of a Circle
(Perimeter of a Circle) (Diameter)x(Pi)
(Area of a Circle) (Radius) (Radius) (Pi)
Pi is the ratio of the circumference of a circle to its diameter. Pi is a number,
approximately 3.14, and is usually represented by the Greek letter .
The figure below is made up of a circle and a polygon. To find the
perimeter of the colored part in the square, first, separate the parts with
straight edges from the parts with curved edges. Use the circumference of
a circle to find the lengths of the curved edges and the total perimeter. In
order to find the area of the colored part, add and subtract the areas of
different parts to obtain the shape of the known area.
Perimeter of the +++= +
Colored Part
Area of the +- =
Colored Part
Example Find the perimeter and the area of the colored 5 cm
part. 5 cm
Class Notes
The total length of the line segments of the colored part is equal to the perimeter of a
square that has sides of cm. The total length of the curved parts is equal to
the perimeter of a circle that has a radius of cm.
Therefore, the perimeter of the colored part is 4 3.14 cm.
When you add the area of the colored parts, the sum is equal to the area of a circle
that has a radius of 5 cm, therefore, 3.14 cm2.
112 NUMINO Challenge D1
