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Hello!
My question: Determine all monotonic functions f defiend on te set of realnumbrs, such that f(x)+2x=f(f(x)). I hope, you can help me, or give me some instructions, how should i begin.
thanks
Hi Grull~
Hmmm...let f(x) = ax so that ax + 2x = f(ax) = a^2x. Now set all that equal to 0. a^2x - ax - 2x = 0 so you have the characteristic equation a^2-a-2 = 0 = (a-2)(a+1) -> a = -1,2 or that ax = -x or 2x. Can you see how you can find the others??
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Sherry Wallin
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