find the circumference of a circle whose area is 4 times the area of circle with diameter 21 CM
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area of circle with diameter 21cm is πr²
(22/7)×(21/2)² = 693/2 = 346.5 cm²
this area is 4 times more so 346.5×4 = 1386
now πr² = 1386 (this is first circle area)
r² = (1386×7)/22 = 441
r = 21 then circumference = 2πr = 2×(22/7)× 21
= 132cm
(22/7)×(21/2)² = 693/2 = 346.5 cm²
this area is 4 times more so 346.5×4 = 1386
now πr² = 1386 (this is first circle area)
r² = (1386×7)/22 = 441
r = 21 then circumference = 2πr = 2×(22/7)× 21
= 132cm
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