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# How to find 3D diagonal length? watch

1. Hiya, I feel like this may be stupidly obvious but I can't think of how to figure out how to find the length between 1 and 3 in the diagram, where a = 201 pm.

Any help would be much appreciated, thanks
2. (Original post by ayelmao)
Hiya, I feel like this may be stupidly obvious but I can't think of how to figure out how to find the length between 1 and 3 in the diagram, where a = 201 pm.

Any help would be much appreciated, thanks
All you need to do is to use Pythagoras in 3 dimensions, so sqrt(a^2+a^2+a^2) = sqrt(3a^2) = sqrt(3)*a

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Updated: January 16, 2017
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