The surface area of a closed rectangular box, which is inscribed in a sphere, is 846 sq cm, and the sum of
the lengths of all its edges is 144 cm. The volume, in cubic cm, of the sphere is
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Explanatory Answer
Given: A closed rectangular box
Step 1: Surface area of the box
2(lb + lh + bh) = 846
Step 2: Sum of the lengths of all edges
4(l + b + h) = 144
=> l + b + h = 144 / 4 = 36 …(1)
Step 3: Square equation (1)
(l + b + h)^2 = l^2 + b^2 + h^2 + 2(lb + lh + bh) = 36^2 = 1296
l^2 + b^2 + h^2 = 1296 − 846 = 450
Step 4: Diameter of the sphere (space diagonal of the box)
d = √(l^2 + b^2 + h^2) = √450 = 15√2 = 2r
Step 5: Radius of the sphere
r = (15√2) / 2 = 15/√2
Step 6: Volume of the sphere
V = (4/3) π r^3 = (4/3) π (15√2 / 2)^3
V = (4/3) π * 1125√2 / 8
V = 1125 π √2 / 6
V = 1125 π √2
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