follow us on facebook and the enlightened elephant blog to receive, updates, links to products and...
DESCRIPTION
LET’S START BY LOOKING AT SOME FEATURES OF CIRCLES! CIRCLESTRANSCRIPT
LET’S START BY LOOKING AT SOME
FEATURES OF CIRCLES!
CIRCLES
CircleA circle is a round figure with all of the points ON the circle the same distance to the center.
A
B
C
D
E
CENTER: The point in the middle of the circle. Click for effects
Diameter: The distance across the circle, through the center. (click for effects)
Radius: The distance from any point on the circle to the center. (click for effects)
Diameter is represented by “d”
Radius is represented by “r”
RADIUS AND DIAMETER
SOME CONCLUSIONS
Let’s look at the
relationship between
radius and diameter!
How are the Radius and Diameter Related?
Diameter
Radius
SO….The radius is half the length of the diameter.
The radius only goes HALFWAY through the circle.
Which means the diameter is twice as long as the radius.
d =2r
r = 1/2d
The diameter goes all the way through the circle.
Let’s Practice!
IDENTIFY THE RADIUS AND DIAMETER OF
CIRCLES
Identify the Length of the Radius
r = 7 cm
7 cm
Distance from a
point on the circle
to the center!
Identify the Length of the Diameter
d = 2r = 14 cm
7 cmThe
diameter is twice as
long as the radius!
Identify the length of the radius
r = 9 cm
9 cm
Distance from a
point on the circle
to the center!
Identify the length of the diameter
d = 2r = 18 cm
9 cm
The diameter is
twice as long as the
radius!
Identify the length of the radius
r = 6 cm
The radius is half the length of
the diameter!
Identify the Length of the Diameter
d = 2r = 2*6 = 12 cm
How will you find
the length of the
diameter?
Identify the Length of the Radius
r = 10 cm
How will you find
the length of the
radius?
NOW LET’S FIND OUT WHAT CIRCUMFERENCE IS!
NICE JOB SO FAR!
Circumference is the distance around a circle. (Click for effects.)
To calculate the circumference:
diameter
rdC 2r = radiusd = diameter
Multiply the
diameter by pi, which is about 3.14!
What is Circumference?radius
Let’s Practice!
FIND THE CIRCUMFERENCE OF
CIRCLES!
Find the circumference
C = cm68.3714.31212
Multiply the diameter by pi, which is about 3.14!
d r2C = =
Find the circumference in terms of pi
C = =
12 cm
r2 12
Don’t use 3.14 for pi,
use the symbol!
d r2C = =
Find the Circumference
cm96.4314.3141472
Multiply the diameter by pi, which is about 3.14!
d r2C = =
Find the circumference in terms of pi
r2 1472 dC = = = cm
Don’t use 3.14 for pi,
use the symbol!
d r2C = =
Find the Circumference
cm52.5614.3181892
d r2C = =
Multiply the diameter by pi, which is about 3.14!
Find the Circumference in Terms of Pi
C = = = cmr2 1892 d
Don’t use 3.14 for pi,
use the symbol!
d r2C = =
NOW LET’S FIND OUT WHAT AREA IS!
You’re Doing Great!
Area of a CircleThe area of the circle is the amount of space that changes color. (click to see).To Find the Area:
2rA
r
d
r = radiusd = diameter
Square the radius and multiply by
pi!
FIND THE AREA OF CIRCLES!
Let’s Practice!
Find the Area
A = 22 86.15314.349497 cm
2rA =
Square the radius and multiply by
pi!
Find the Area in terms of pi
A = = 49722r 2cm
Don’t use 3.14 for pi,
use the symbol!
2rA =
Find the Area
A = 22 96.20014.364648 cm
2rA =
Find the radius first! Square it,
then multiply by pi!
Find the Area in terms of pi
A = 6482 2cm
Don’t use 3.14 for pi,
use the symbol!
2rA =
Find the Area
A = 22 31414.310010010 cm
Find the radius first! Square it,
then multiply by pi!
2rA =
Find the Area in Terms of Pi
A = 100102 2cm
Don’t use 3.14 for pi,
use the symbol!
2rA =
Find the Area
A = = 22 5.7814.325255 cm 2r
Find the radius first! Square it,
then multiply by pi!
2rA =
CIRCUMFERENCE AND AREA
Let’s Review!
CIRCUMFERENCE of a Circle
1. What is the circumference of a circle?A)Distance Around the CircleB)Amount of Space on the Circle
2. To find the circumference, you need to know or calculate the __________.
A)RadiusB)Diameter
B) Diameter
A) Distance Around
AREA of a circle
1. What is the area of a circle?A)Distance Around the CircleB)Amount of Space on the Circle
2. To find the area, first you need to know or calculate the…?
A) RadiusB) Diameter
A) Radius
B) Amount of Space
THE END!
GREAT JOB!Now you know all about
circles!