Assume f(x)'s coefficients are all real;

Otherwise there is no unique solution.

Let f(x) = a(x-2)(x-b), where a and b are real to be determined. f(f(x)) has only one real zero 5, then 5 must be a multi-root. Then either f(x) - 2 = a(x-5)(x-5) or f(x) - b = a(x-5)(x-5) ( b cannot be 2....) . Now we almost done.

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• 回复：Assume f(x)'s coefficients are all real; -jinjing- ♀ (247 bytes) () 07/13/2011 postreply 20:37:56

• Did not read this before send my post, which is the same. -wxcfan123- ♂ (0 bytes) () 07/15/2011 postreply 16:41:21