Find all functions f: (0,∞)------ (0,∞) such that
f(f(f(x))) + 4f(f(x)) + f(x) = 6x .
I suspect f has to be linear. If so, let, and youll find that there are only three possibilities: , , .
I dont know if f can be non-linear (though I have a hunch that it cant).
So f must be injective. Thats another thing we can say about the function.
thank you jane
but i think The only solution of function is f(x) = x,
what can be easily checked.
Last edited by tony123 (2008-07-23 04:49:41)