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# Radius, diameter, and circumference and area of Circles

A circle is a plane round figure in which all points are equidistant from the center.

Radius is a line segment that joins the center of circle to any point on the circumference of circle.

Diameter is a straight line segment passing through the center of circle, the endpoints of which touches the circumference of circle.

Circumference of circle is the distance around the circle.

Circumference of circle = 2π× radius = π× diameter

Area of circle = π× (radius)2

Example:What is the radius of circle with diameter 12 inches?

Radius of circle =   =   = 6 inches

Example:If the circumference of circle is 88 cm, then what is the radius of circle? (Use π= )

r = 88

2 ××r = 88 implies r = 14 cm

#### Check Point:

1. What is the radius of circle with circumference 24π in?
2. What is the area of circle with circumference 30.2 yards? Round your answer to the nearest tenth. (Use π = 3.14)
3. What is the area of circle with diameter 6 yards? Round your answer to the nearest tenth. (Use π = 3.14)
4. What is the diameter of circle with circumference 63 feet? Round your answer to the nearest whole. (Use π = 3.14)
5. What is the circumference of circle with area 12.6 in2? Round your answer to the nearest tenth. (Use π = 3.14)
1. 12 in.
2. 6 yd2
3. 3 yd2
4. 20 feet
5. 6 in

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