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Monday, July 5, 2021

Cover the plane with strips

 In the 2D plane, a strip is the space between (and including) two parallel lines (which extend to infinity in both directions). The width of a strip is the distance between the two parallel lines that make up a strip. The width of a strip is non-zero (otherwise we just call it a line).


Can you fully cover the 2D plane with strips the sums of whose widths is finite? (Proof required of course).



Scroll down for a solution.



Consider a circle of radius R. A strip of width wi can cover an area at most 2wiR.


So strips of total width w (infinite number of strips or not), can cover at most an area of 2wR.


For sufficiently large R, πR2>2wR. So we cannot cover the plane with strips the sum of widths of which is finite.

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