[問題] Dumb questions

[pikahacker (死亡筆記 型電腦)]

1. Prove that there exists a UNIQUE function f from set R+ to R+ such that
   f(f(x))=6x-f(x)

2. For every n in Z+, let Rn be the minimum value of |c-d*3^(1/2)| for all
   nonnegative integers c and d with c+d=n.  Find, with proof, the smallest
   positive real number g with Rn < or = g for all n in Z+.


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推 darkseer:這是?
推 pikahacker:Putnam1988,做了半天被這兩題卡住@___@"