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Positively Real (Posted on 2012-09-09) Difficulty: 3 of 5
R+denotes the set of positive real numbers.

Determine all possible functions f:R+ R+ such that:

f(f(x)) = 12x - f(x) for all x > 0.

No Solution Yet Submitted by K Sengupta    
Rating: 5.0000 (1 votes)

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Some Thoughts re: Explanation of my solution. Comment 4 of 4 |
(In reply to Explanation of my solution. by Chris, PhD)

if f(x) = ax + c, and a >0, and the function maps from R+ to R+, then c must be 0, because nothing would otherwise map into the interval (0,c].  
  Posted by Steve Herman on 2012-09-10 08:46:21

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