Answer
$(g ∘ g)(x) = (x^2 - 2)(x^2-6)$
the domain is $(-\infty,\infty)$
Work Step by Step
$g(x) = x^2-4$
$(g ∘ g)(x) = g(g(x)) = g(x^2-4) = (x^2-4)^2 -4= x^4-8x^2+16 -4=x^4-8x^2+12=(x^2 - 2)(x^2-6)$
Therefore (the function is polymoial) the domain is $(-\infty,\infty)$
