Answer:
[tex]x^{4}[/tex] + 2x² + 2
Step-by-step explanation:
To obtain f(f(x)), substitute x = f(x) into f(x), that is
f(f(x)) = f(x² + 1) = (x² + 1)² + 1 = [tex]x^{4}[/tex] + 2x² + 1 + 1 = [tex]x^{4}[/tex] + 2x² + 2
