The stationary point at x = x */2 (found by setting that the first derivative of x * x − f (x) with respect to x equal to zero) is in the domain [2, 3] if and only if 4 ≤ x * ≤ 6. Otherwise the maximum is taken either at x = 2 or x = 3 because the second derivative of x * x − f (x) with respect to x is negative as − − 2 ; for a part of the domain x ∗ ∗ < 4 the maximum that x * x − f (x) can take with respect to x ∈ ∈ [ 2 , 3 ] is obtained at x = 2 while for x ∗ ∗ > 6 it becomes the maximum at x = 3 . Thus, it follows that f ∗ ∗ ( x ∗ ∗ ) = { 2 x ∗ ∗ − − 4 , x ∗ ∗ < 4 x ∗ ∗ 2 4 , 4 ≤ ≤ x ∗ ∗ ≤ ≤ 6 , 3 x ∗ ∗ − − 9 , x ∗ ∗ > 6.