Circles
October 27, 2015
Geometry Chapter 1 LAST DAY!!
Test on Thursday. That means ALL HOMEWORK
must be graded and turned in by Wednesday
afternoon!
OBJ: To find the circumference(perimeter) and area of
circles.
Formulas:
C = 2πr
A= πr2
C = πd
circumference
is the same as
perimeter
diameter
ra
diu
s
2 r=d
π
Circles
October 27, 2015
Ex: Find the area and circumference of a circle with
a radius of 9 feet. Express the answer in terms of
rounded to the nearest 10th,
rounded to the nearest 100th.
First: Draw and label a figure.
Second: Write formulas(find and state r )
Third: Fill in formula
C = 2 πr
or
C = πd
A = πr
C = 2π r
A = πr
C = 2 π9
C = 18π
A = π92
A = 81π
Why this formula?
π (exact ans),
9 feet
2
2
Finally write answers in correct form.(with label)
You will directed on how to write answers.
C = 18π ft
C = 56.5 ft
C = 56.55 ft
EXACT
NEAREST 10TH
NEAREST 100TH
A = 81π ft2
A = 254.5 ft2
A = 254.47 ft2
Circles
October 27, 2015
First: Draw and label a figure.
Second: Write formulas(you will have to choose the correct one for circumference)
Third:Fill in formula
C = 2π r
C = πD
A = πr2
ex: r = 4 mi
C = 2π
A=π
C=
A=
π
2
π
π
Finally write answers in correct form.(with label)
C=
C=
C=
π ft
ft
ft
EXACT
NEAREST 10TH
NEAREST 100TH
A=
A=
A=
π ft2
ft2
ft2
Circles
October 27, 2015
ex: d = 12 yd
Finally write answers in correct form.(with label)
C=
C=
C=
EXACT
NEAREST 10TH
NEAREST 100TH
A=
A=
A=
πydft2
yd
ft2
yd
ft2
Circles
October 27, 2015
ex: d = 7 ft
Find the circumference and area.
Give exact answers.
π
Assign: WKSHT ON CIRCLES
Draw and label fig, write each formula, fill in formula
give answers in specified form(with label)
Circles
October 27, 2015
Find the circumference and area to
the nearest 10th.
20mi
Circles
October 27, 2015