circles & circumference 8 th grade pre-algebra circles & circumference ppt molly thompson
TRANSCRIPT
Circles &
Circumference
8th Grade Pre-AlgebraCircles & Circumference PPT
Molly Thompson
Parts of a Circle
• Circle: the set of all points in a plane that are an equal distance from a fixed point, called the center
• Circumference: the distance around the circle
radius
diameter
chord
Circumference, Diameter & π
• Pi (π) is the ratio of the circumference of a circle divided by its diameter. The value of pi is approximately 3.14.
C ≈ πd
• If the diameter of a circle is 10 in., then the circumference would be 31.4 in.
d= 10 in.
The Circumference Formula
• The formula for finding the circumference of a circle is… C ≈ πd. – To find the circumference, multiply 3.14 by the
value of the diameter
• C ≈ π d• C ≈ (3.14)(3 cm)• C ≈ 9.42 cm• The distance around the circle is 9.42 cm.
d = 3 cm
Circumference Examples
• Find the circumference of a circle with a diameter of 5.5 meters
C ≈ π dC ≈ (3.14)(5.5 m)C ≈ 17.27 m
Circumference Examples
• Find the circumference of a circle with a radius of 15 inches Since it takes two radii to make the diameter, 2(15) means the diameter is 30 inches.
C ≈ π dC ≈ (3.14)(30 in)C ≈ 94.2 inches
Real-life Circumference Example
Big Ben is a famous clock tower in London, England. The diameter of the clock face is 23 feet.
Find the circumference of Big Ben’s clock face.
C ≈π dC ≈ (3.14)(23 ft)C ≈ 72.22 feet