That is not enough information.
If you look at the graphic, diagonal BD (along with point E), can be moved up and down the long diagonal and the two diagonals will still have the same length. You need to state additional information.
Answer:
~8.66cm
Step-by-step explanation:
The length of a diagonal of a rectangular of sides a and b is

in a cube, we can start by computing the diagonal of a rectangular side/wall containing A and then the diagonal of the rectangle formed by that diagonal and the edge leading to A. If the cube has sides a, b and c, we infer that the length is:

Using this reasoning, we can prove that in a n-dimensional space, the length of the longest diagonal of a hypercube of edge lengths
is

So the solution here is

Answer:
The length of AC = 4 and the length of A'C' = 1 so the scale factor is 1/4.
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