How do you find inner diagonals of a cube? I was wondering that for a very long time.

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- Feb 16th 2013, 05:29 PMevilgummybearInner diagonals?
How do you find inner diagonals of a cube? I was wondering that for a very long time.

- Feb 17th 2013, 12:42 AMveileenRe: Inner diagonals?
http://img850.imageshack.us/img850/9131/frtitluu.jpg

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: