Circle:
What is a radius?
(plural = radii)
A line segment with one endpoint at the
center of the circle and the other endpoint
on the circle
What is a chord?
A line segment with both endpoints on a
circle
What is a diameter?
A chord that passes through the center of
the circle – reaching from one side of the
circle to the other (d=2r)
What is circumference?
The circumference is the distance around
the circle.
(Relate it to the perimeter of a polygon.)
What is pi?
How do I find the
circumference of a circle?
Find the circumference of the
following circle:
8ft
The ratio of the circumference to the
diameter, c/d, is the same for ANY circle –
and is represented by the Greek letter  read “pi”.
Pi starts with 3.14159265… and goes on
forever without repeating. It is called
We use 3.14 or 22/7 to represent this value.
Circumference = d or 2r
 = 3.14 or 22/7
d= diameter
r= radius
Find the circumference of the
following circle:
3 cm
Circumference = 37.68 inches
Find the diameter and radius
How do I find the area of a circle?
The formula for area is A = x r2
You can use 3.14 or 22/7 for pi.
Example 1
Find the area of the circle. Use 22/7 for pi.
D= 14 in. A = ??
1.
2.
14 in.
A =  x r2
r = d/2
r = 14/2=7
A = 22/7 x 72
A = 22/7 x 49
A = 154 in. 2
Example 2
3.
4.
5.
write the formula to find area.
the length of the diameter is 2
times the radius, so divide the
diameter by 2.
replace pi with 22/7 and r with
7.
Simplify, then multiply
Area is measured in square
units.
Find the area of the circle. Use 3.14 for pi.
A =  x r2
A = 3.14 x 32
A = 3.14 x 9= 28.26 cm2
3cm
Practice #1
Find the area of the circle.
R = 21 A = ??? (1,386 cm2)
Practice #2
Find the area of the circle. Use 3.14 for pi.
D = 10m A = ??? (78.50m2)
Circle:
What is a radius?
(plural = radii)
A line _______________________ with
one _________________ at the
_____________ of the
_________________ and the other
___________________ on the circle
What is a chord?
A line _________________t with
______________ endpoints on a
___________.
What is a diameter?
A ____________________ that passes
through the ______________ of the circle
– reaching from one ______________ of
the circle to the other (d=______)
What is circumference?
The circumference is the distance
_______________the circle.
(Relate it to the perimeter of a polygon.)
What is pi?
How do I find the
circumference of a circle?
The _____________________ of the
circumference to the diameter, c/d, is the
same for _______________ circle – and is
represented by the Greek letter  - read
“pi”.
Pi starts with 3.14159265… and goes on
forever without ___________________.
We use ________________ or
_______________ to represent this value.
Circumference = ________ or _________
 = ___________ or ___________
d= _____________________
r=____________________
Find the circumference of the
following circle:
8ft
Find the circumference of the
following circle:
3 cm
Circumference = 37.68 inches
Find the diameter and radius
How do I find the area of a circle?
The formula for area is A = x r2
You can use 3.14 or 22/7 for pi.
Example 1
Find the area of the circle.
D= 14 in. A = ??
Example 2
Find the area of the circle. Use 3.14 for pi.
3 cm
Practice #1
Find the area of the circle.
R = 21 A =
Practice #2
Find the area of the circle. Use 3.14 for pi.
D = 10m A = ???