Clue to Puzzle #44: Diagonals on the Face of a Cube. What's the Angle?

I propose to give clues here in the form of diagrams, the idea will be to reveal them one at a time until the answer is clear. Be sure to examine the cube in the question carefully first. If you're running through some advanced trig in your mind you're barking up the wrong tree.
Where next?
Questions Answer

Where next?
Questions Answer
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