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

# daily puzzle

Started by ●September 14, 2020

Reply by ●September 14, 20202020-09-14

On Monday, September 14, 2020 at 2:49:51 PM UTC-7, RichD wrote:> 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?Maybe closer to the subject of this group, what is the symmetry of the 111 face of a silicon crystal. (Or any cubic crystal.) With the right coordinate system, the coordinates of the points in question are [110], [101], and [011]. However, the answer is even easier, as there is only one angle that is a possible solution, and that we should know without the need to look it up.

Reply by ●September 15, 20202020-09-15

On Tuesday, September 15, 2020 at 6:49:51 AM UTC+9, RichD wrote:> 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 - > > -- > Rich60 deg?