Area of a Circle
Radius, Diameter & Circumference of a Circle
100
What is the "radius" of a circle?
The distance from the centre of the circle to a point on the circle
100
What is the "circumference" of a circle?
The distance around a circle OR the perimeter of a circle
200
Find the area of this circle:
A=ᴨr2
A=(3.14)(4 cm)2
A=(3.14)(4 cm)(4 cm)
A=50.24 cm2
200
What is the "diameter" of a circle?
The distance across a circle through its centre
300
Find the area of this circle:
A=ᴨr2
A=(3.14)(12 cm)2
A=(3.14)(12 cm)(12 cm)
A=452.16 cm2
300
What is the circumference of this circle?
C=2ᴨr
C=(2)(3.14)(3 cm)
C=18.84 cm
400
The diameter of a circle is 12 in. Find the area of the circle:
r = d
2
r=12 in
2
r=6 in
A=ᴨr2
A=(3.14)(6 in)2
A=(3.14)(6 in)(6 in)
A=113.04 in2
400
What is the circumference of this circle? (" is inches)
C=ᴨd
C=(3.14)(8 in)
C=25.12 in
500
Ms. K was trying to find the area of this circle but she made a mistake:
What mistake did she make in her work shown below? What is the correct answer?
A=ᴨr2
A=(3.14)(5 cm)2
A=(3.14)(5 cm)(2)
A=31.4 cm2
She multiplied the radius by 2 instead of squaring it.
A=ᴨr2
A=(3.14)(5 cm)2
A=(3.14)(5 cm)(5 cm)
A=78.5 cm2
500
The circumference of a circle is 69.08 ft. What is the radius of the circle?
C=ᴨd
69.08 ft=(3.14)(d)
3.14 3.14
22 ft=d
r = d
2
r = 22ft
2
r = 11 ft