The radius of an outer circle is 21cm and the inner circle is 14cm. Find the area of an cricular ring.
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Answer:
The distance around the circular region is called its circumference. The ratio of circumference of any circle to its diameter is constant. This constant is denoted by π and is read as pie.
Circumference/Diameter = Pie
i.e., c/d = π or c = πd
We know that diameter is twice the radius, i.e., d = 2r
C = π × 2r
⇒ C = 2πr
Therefore approximate value of π = 22/7 or 3.14.
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The area of ring will be = area of large circle - small circle
let say larger radius is R1 = 21cm and smaller circle radius R2 = 14
Therefore are of ring = πR1² - πR2²
= π (r1²-r2²)
= π (441-196)
= π × 245
take π = 22/7 here
= 22×245/7
= 770 cm²
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