MathDB
"game" on the plane

Source: 2022 China Southeast Grade 10/11 P8

August 3, 2022
combinatoricswinning strategy

Problem Statement

Tao plays the following game:given a constant v>1v>1;for any positive integer mm,the time between the mthm^{th} round and the (m+1)th(m+1)^{th} round of the game is 2m2^{-m} seconds;Tao chooses a circular safe area whose radius is 2m+12^{-m+1} (with the border,and the choosing time won't be calculated) on the plane in the mthm^{th} round;the chosen circular safe area in each round will keep its center fixed,and its radius will decrease at the speed vv in the rest of the time(if the radius decreases to 00,erase the circular safe area);if it's possible to choose a circular safe area inside the union of the rest safe areas sometime before the 100th100^{th} round(including the 100th100^{th} round),then Tao wins the game.If Tao has a winning strategy,find the minimum value of 1v1\biggl\lfloor\frac{1}{v-1}\biggr\rfloor.