Circumference of the circle or perimeter of the circle is the measurement of the boundary of the circle. The area of a circle is π multiplied by the square of the radius. The area of a circle(A) when the radius 'r' is given is πr^2. π is approx 3.14 or 22/7.
1. Parts of a Circle Area & Circumference
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3. RADIUS = ½ OF DIAMETER If the radius is 5 cm, what is the diameter? 10 If the diameter is 32 ft, what is the radius? cm 16 ft 58 cm 78 cm What is the What is the diameter? 116 radius? 39 cm cm
4. CIRCUMFERENCE OF A CIRCLE Formula is C = 2r (2 x Pi x Radius) or C = d (Pi x Diameter) Remember… = 3.14 (approximately) *You can use either formula depending on what they give you in the original problem
5. The circumference of a circle Use π = 3.14 to find the circumference of the following circles: C = πd 9m C = 2πr 4 cm = 3.14 × 4 = 2 × 3.14 × 9 = 12.56 cm = 56.52 m C = πd C = 2πr 58 cm 23 mm = 3.14 × 23 = 2 × 3.14 × 58 = 72.22 mm = 364.24 cm
6. AREA OF A CIRCLE Formula is A = r2 (Pi x Radius Squared) radius
7. The area of a circle Use π = 3.14 to find the area of the following circles: 2 cm A = πr2 A = πr2 10 m = 3.14 × 2 2 = 3.14 × 52 = 12.56 cm2 = 78.5 m2 A = πr2 A = πr2 78 cm 23 mm = 3.14 × 232 = 3.14 × 392 = 1661.06 mm2 = 4775.94 cm2
8. Finding the Radius or Diameter • Circumference • Area C = 5 in. A = 8.9 m2 Calculate the diameter… Calculate the radius…
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