Question 1028661
{{{f(f(x)) = f(x^2-2x) = (x^2-2x)^2 - 2(x^2-2x) = x^4 - 4x^3+2x^2+4x}}}.

This is supposed to be equal to {{{f(x) = x^2 - 2x}}}

==> {{{x^4 - 4x^3+2x^2+4x = x^2 - 2x}}}

<==> {{{x^4 - 4x^3+x^2+6x = 0}}}

<==> {{{x(x+1)(x-2)(x-3) = 0}}}  (Verify!!)

==> The real numbers x such that f(x) = f(f(x)) are 0, -1, 2, and 3.