## Not hard Calculus exercise [closed]

If $$(f \circ g \circ f)(x)=x, \forall x \epsilon \mathbb{R}$$ then show that $$(f \circ g)(x)=( g \circ f)(x)$$

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This site is for research-level mathematics, not calculus exercises. Please see the FAQ for suggestions of sites that are more appropriate for your question. – Andreas Blass Nov 30 2011 at 15:55
(@Steve: Unfortunately, it seems you choose quite an unsuitable title. Actually here's better to avoid "Not hard". Better not to mention " Calculus" here, too. Actually, "exercise" also is not a good world). – Pietro Majer Nov 30 2011 at 17:34
Also, it has nothing to do with calculus: the fact that $x$ is a real number is totally irrelevant. – Thierry Zell Nov 30 2011 at 17:43