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प्रश्न
A lawn is in the shape of a semi-circle of diameter 42 m. The lawn is surrounded by a flower bed of width 7 m all around. Find the area of the flower bed in m2 .
उत्तर
Diameter of the inner semi-drde = 42 m
Hence, radius of the inner semi-circle = r = 21 m
Width of the flower bed = 7m
Diameter of the outer semi-circle = ( 42 + 2 x 7) m = 56 m
Hence, radius of the outer semi-circle= R = 28 m
Area of the semicircular flower bed =Area of outer semi-cirde - area of inner semi-drde
`= 1/2 pi "R"^2 - 1/2 pi "r"^2`
`= 1/2 pi ("R"^2 - "r"^2)`
`= 1/2 xx 22/7 xx (28^2 - 21^2)`
`= 1/2 xx 22/7 xx (784 - 441)`
`= 1/2 xx 22/7 xx 343`
= 539 m2
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