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2006 SMT/Geometry Problems/Problem 1
Problem
Given a cube, determine the ratio of the volume of the octahedron formed by connecting the centers of each face of the cube to the
volume of the cube.
Solution
Let the side length of the square be . Consider
Thus,
. It's an isosceles right triangle with hypotenuse
, and the side length of the octahedron is
and legs of length
.
.
Now consider the top half of the octahedron. It's a pyramid with a square base of length
and height
, and the volume of the entire octahedron is twice this, or
Finally, the ratio of the volume of the octahedron to the volume of the cube is
. Therefore, its volume is
.
.
See Also
2006 SMT/Geometry Problems
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