Transcript circumference

Circumference and area of
circles
Pick up your calculator for today’s notes
The parts of a circle
Radius
Center
Diameter
Circumference
d = 2r
or
r=d÷2
Pi () is an irrational number that is
often approximated by the rational
numbers 3.14 and
22
7
.
The circumference of a circle is the
distance around the circle.
The area of a circle is the number
of square units needed to cover
the circle.
Find the circumference of each circle, both in terms of 
and to the nearest hundredth. Use 3.14 for .
A. Circle with a radius of 4 m
= 2(4)
= 8 m
= 8 * 3.14
= 25.12 m
B. Circle with a diameter of 3.4 ft
=  (3.4)
= 3.4 ft
= 3.4 * 3.14
= 10.676 ft
= 10.68 ft
C = 2r
4m
C = d
3.4 ft
Find the area of each circle, both in terms of  and to the
nearest hundredth. Use 3.14 for .
A. Circle with a radius of 4 in.
A =  (42)
= 16 in2
A =  r2
4in
= 16 * 3.14
= 50.24 in2
B. Circle with a diameter of 3.4 m
d
= 1.7
2
=  (1.72)
= 2.89 m2
= 2.89 * 3.14
= 9.0746 m2
= 9.07 m2
A = r2
3.4 m
What is the circumference of a circle with a diameter of
56 feet? Use 22 for .
7
C = d
56 ft
=  (56)
= 22 (56)
7
= 22 56
1
1 7
= 22
1
8
1
= 176 ft
8
Remember, we are
multiplying so we are
allowed to cancel
before getting our
answer