Let  `f : [0, ∞) → R, \ f(x) = x^2 + 1`.

The equation  `f(f(x)) = (185)/(16)`  has real solution(s)

1.  `x = ± (sqrt13)/(4)`
2.  `x = (sqrt13)/(4)`
3.  `x = ± (sqrt13)/(2)`
4.  `x = (3)/(2)`
5.  `x = ± (3)/(2)`

The function  `f`  satisfies the functional equation  `f (f (x)) = x`  for the maximal domain of  `f.`

The rule for the function is

1. `f(x) = x + 1`
2. `f(x) = x - 1`
3. `f(x) = (x - 1)/(x + 1)`
4. `f(x) = log_e (x)`
5. `f(x) = (x + 1)/(x - 1)`

Which one of the following functions satisfies the functional equation  `f (f(x)) = x`  for every real number `x?`

1. `f(x) = 2x`
2. `f(x) = x^2`
3. `f(x) = 2 sqrt x`
4. `f(x) = x - 2`
5. `f(x) = 2 - x`