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Question
Find the radius of a sphere whose surface area is equal to the area of the circle of diameter 2.8 cm
Solution
Diameter of circle = 2.8 cm ⇒ radius = r = 1.4 cm
Area of a circle = `pir^2`
= `pi(1.4)^2`
= `1.96pi`
Surface area of sphere = `4pir^2`
Given ,
Surface area of sphere = Area of the circle
⇒ `4pir^2 = 1.96pi`
⇒ `r^2 = 1.96/4`
⇒ `r^2 = 0.49`
⇒ `r = 0.7 "cm"`
Radius of the sphere = 0. 7 cm
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