Warm Ups
The height of a trapezoid is 7 meters. The
bases are 16 m and 20 m. Find the area
of the trapezoid.
126 m2
10.7 Circumference and Area Circles
pages 533-538
Circumference- The distance around the
circle.
pi- the ratio of the circumference to its
diameter. We use the greek symbol . We
use 3.14 to represent pi.
chord- a line segment connecting 2 points
on the circle but does not pass through the
center.
arc- a part of a circle named by its
endpoints.
ci r
ference
cum
arc
ord
ch
diamete
r
radius
Finding the Circumference of a circle
C=
d
or
C=2
r
Tip: If you know the diameter, use the
formula with "d".
If you know the radius, use the formula
with "r".
12 m
Find the circumference of
a swimming pool with a
radius of 12m.
C=2 r
C=2(3.14)12
C 75.36 m
The distance around the swimming
pool is about 75 meters.
Finding the diameter of a circle
The circumference of a circle is 90 ft. Find
the diameter of the circle to the nearest
foot.
C= d
90=3.14d
90=3.14d
3.14 3.14
28.66242 = d
28.7 d
The diameter of the circle is about 29 ft.
How would you find the radius???
A=
r2
9cm
Finding the AREA of a circle
A= r2
A = 3.14(92)
A = 3.14(81)
A 254.34 cm
The area of the circle is about 254 cm2.
Finding the Radius of a circle
The area of a circle is 250 in2. Find the
radius to the nearest inch.
A= r2
250 = 3.14 r2
250 = 3.14 r2
3.14 3.14
79.617 = r2
79.617 = r2
8.9 = r
9 r
The radius is about 9 in.