Let f(x) = x^2 - 2x. What is the value of f(f(f(f(f(f(2))))))?
f(2) = 2^2 - 2(2) = 0
Note that, from here on, every evaluation of the nested functions will = 0 because f(0) = 0
So
f(f(f(f(f(f(2)))))) = 0