SOLUTION: Two spheres of equal radius are taken out by cutting from a solid cube of side 13cm. What is the maximum volume(in cm^3) of each sphere.

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Question 1114815: Two spheres of equal radius are taken out by cutting from a solid cube of side 13cm. What is the maximum volume(in cm^3) of each sphere.
Found 2 solutions by MathLover1, ikleyn:
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

If sphere is inscribed in a cube, the diameter of the sphere is equal to the length of cube’s edge.
Since you have 2 spheres taken out by cutting from a solid cube (they are actually inscribed in cube) then the side of the cube equal to the sum of their diameters which are equal in length.
so, you have
2d=13cm
d=13cm%2F2
the length of the each radius is:
r=d%2F2
r=%2813cm%2F2%29%2F2

r=13cm%2F4
r=3.25cm
the maximum volume of each sphere is:
V=%284%2F3%29pi%2Ar%5E3
V=%284%2F3%29pi%2A3.25%5E3
V=%281.333333333333333%29pi%2A34.328125
V=45.77pi
V+143.7178

Answer by ikleyn(52787) About Me  (Show Source):
You can put this solution on YOUR website!
.
I read and interpret the condition by different way: two spherical solids are taken out by cutting from a solid cube
in a way that their centers are located on the  3D  (=longest) diagonal of the cube.



        (This condition provides the maximum radius and maximum volume to each of the two spheres).



Then it is clear that these spheres touch each other at the middle of the  3D  diagonal of the cube.


The length of the longest 3D diagonal of this cube is   13%2Asqrt%283%29 cm.


If "r" is the radius of the sphere, then    r%2Asqrt%283%29%2Br = 6.5%2Asqrt%283%29 cm.


Hence,    r = %286.5%2Asqrt%283%29%29%2F%281+%2B+sqrt%283%29%29 = 4.12 cm.


Then the volume of each sphere    V = %284%2F3%29%2Api%2Ar%5E3 = %284%2F3%29%2A3.14%2A4.12%5E3 = 292.8 cm^3.

Solved.