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Circles
Learn to find the area and circumference of circles.
A circle is the set of points in a plane that are a fixed distance from a given point, called the center.
A radius connects the center to any point on the circle.
A diameter connects two points on the circle and passes through the center.
Radius
CenterDiameter
Circumference
The diameter d is twice the radius r.
d = 2r
The circumference of a circle is the distance around the circle.
A. Circle with a radius of 4 m
C = 2pr= 2p(4)
= 8 p m
B. Circle with a diameter of 3.3 ft
C = pd= p(3.3)
= 3.3 p ft
Find the circumference of each circle in terms of
.4m
3.3ft
A = pr2 = p(42)= 16 p in2
A. Circle with a radius of 4 in.
Find the area of each circle in terms of .p
B. Circle with a diameter of 3.3 m
A = pr2 = p(1.652)
= 2.7225p m2
d2 = 1.65
4in
3.3m
Tweedle Dum & Tweedle Dee will help you remember your
circle formulas!
Tweedle Dum and Tweedle Dee
Around the circle is pi times d.
And if the area is declared
Then its pi r squared.
A = pr2
= p(32)
= 9 p units2
C = pd
= p(6)
= 6 p units
Graph the circle with center (–2, 1) that passes through (1, 1). Find the area and circumference, in terms of .p
C = pd = p(56)
176 ft (56) 22 7
22 7
A Ferris wheel has a diameter of 56 feet and makes 15 revolutions per ride. How far would someone travel during a ride? Use for p.
Find the circumference.
56 1
22 7
The distance is the circumference of the wheel times the number of revolutions, or about 176 15 = 2640 ft.
Lesson Quiz
Find the circumference of each circle in terms of .p
1. radius 5.6 m
2. diameter 113 m
11.2 p m
113 p mm
Find the area of each circle in terms of p.
3. radius 3 in.
4. diameter 1 ft
9 p in2
0.25 p ft2