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Circumference of a Circle

Circumference of a Circle. Math 10-3 Ch.3 Measurement. Properties of Circles…. Yesterday we talked about the perimeter of various 3 sided and 4 sided shapes. How do we find the perimeter of a circle? First, let’s review the properties of the circle:

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Circumference of a Circle

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  1. Circumference of a Circle Math 10-3 Ch.3 Measurement

  2. Properties of Circles… • Yesterday we talked about the perimeter of various 3 sided and 4 sided shapes. How do we find the perimeter of a circle? • First, let’s review the properties of the circle: • *All the points on a circle are equidistant (the same distance) from the CENTER of the circle.

  3. Properties of Circles… • *A line that passes through the center of a circle and touches the edge of the circle on both sides is called the diameter.

  4. Properties of Circles… • *A line that starts at the center of the circle and touches an outside edge is called the radius.

  5. Diameter and Radius… • *The radius can be calculated by dividing the diameter by 2 • *The diameter can be calculated by multiplying the radius by 2

  6. *The circumference of a circle is the perimeter of the circle. It can be calculated with the formula : • Where • C = circumference (perimeter) • = “pi” a constant that is 3.14159…. • d = diameter

  7. Ex1. What is the circumference of a circle with a diameter of 8 cm? • C = ? • d= 8cm • C = x 8 • C = 3.14 x 8 *note: we will use the estimation of 3.14 for pi in this course • = 25.12 cm

  8. Ex2. What is the circumference of a circle with a radius of 2.5 mm? • C = ? • d= ? • r = 2.5 mm • *first we must find the diameter of the circle. • d = 2 x r • d= 2 x 2.5 mm = 5 mm

  9. Ex2. What is the circumference of a circle with a radius of 2.5 mm? • C = x 5 • = 3.14 x 5 • = 15.7 mm

  10. Ex3. The circumference of a circle is 52cm. What is the diameter? • C = 52 cm • d = ? • *We must perform opposite operations (algebra!) to calculate the diameter! • First, fill in the formula with what we know: • 52 cm = 3.14 x d • What is opposite of multiplying by 3.14? Dividing by 3.14 on the other side! • 52 cm 3.14 = d • d = ~16.56 cm

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