How do you find inner diagonals of a cube? I was wondering that for a very long time.
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Let a be the length of every side. D'B is an inner diagonal of the cube ABCDA'B'C'D'. B'D, A'C, C'A are also inner diagonals.
DD' (ABCD), so DD' is perpendicular to DB (since DB is in (ABCD)), that means that BDD' is a right triangle:
ABD is a right triangle, so:
Last edited by veileen; February 17th 2013 at 12:45 AM.
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