A quickie. No diagram, but no need.
Given a unit cube, vertices labeled ABCD on the top face, EFGH on the bottom; where A E, B F, etc. Draw diagonals GD and BD, across the appropriate faces.
What is the angle GDB?
You have two minutes, no calculator, pen and paper only -
-- Rich
45 degrees...
Chris
60 degrees.
BD, BG and DG are all diagonals of a square, so it's an equilateral triangle.
CH
Yep, but if you don't see that, the dot product of the simple vectors gives the same answer.
60 degrees it's an equilateral triangle.
GDBE is a regular tetrahedron,
-- Jasen.
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