Answer:
(g•f)(x) = x.
Step-by-step explanation:
Let [tex]f(x) = x^{2} + 1[/tex], then the inverse function of the f(x) is [tex]g(x) = \sqrt{x - 1}[/tex]
So, (g•f)(x) = [tex]g[f(x)] = g(x^{2} + 1 ) = \sqrt{(x^{2} + 1) - 1} = \sqrt{x^{2} } = x[/tex]
Therefore, we can write if f(x) and g(x) are inverse functions of each other, then (g•f)(x) = x.
Hence, option D is correct. (Answer)