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
Correct Answer :
1125 π√2
Solution :
The correct option is 1125 π√2.
Let the dimensions (length, width, and height) of the inscribed rectangular box be represented by , , and .
We are given the following information about the rectangular box:
1. The sum of the lengths of all its edges is 144 cm.
2. The total surface area of the box is 846 sq cm.
Step 1: Express the sum of the dimensions
A rectangular box has 12 edges in total (4 lengths, 4 widths, and 4 heights). Therefore, the sum of all its edges is:
Dividing both sides by 4 gives:
Step 2: Express the total surface area
The total surface area of a closed rectangular box is given by:
Step 3: Relate the box dimensions to the sphere's radius
Since the rectangular box is inscribed in a sphere of radius , the space diagonal of the box is equal to the diameter of the sphere (). Using the 3D Pythagorean theorem, the space diagonal is:
Squaring both sides, we get:
We can find the value of using the algebraic identity:
Substituting the known values from Steps 1 and 2:
Subtract 846 from both sides:
Solve for :
Taking the square root of both sides gives the radius of the sphere:
Step 4: Calculate the volume of the sphere
The volume of a sphere is given by:
Substitute the radius :
Simplifying the constant terms:
Multiply the numerator and denominator by to rationalize the denominator:
Therefore, the volume of the sphere is 1125 π√2 cubic cm.
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