James Burkett Hartle, Gravity: An Introduction to Einstein's General Relativity, 2nd edition
Chapter 2. Geometry as Physics 제2장. 물리학으로서의 기하학
문제(Problem) 1 및 해설(Solution)
(a) In a plane, show that a light ray incident from any angle on a right-angle corner reflector returns in the same direction from whence it came.
(b) Show the same thing in three dimensions with a cubical corner reflector.
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