Question 743599
f(g(x)) is a composition - we take a function as an input to another function.

{{{f(x)= x^2+7}}}

and 

{{{g(x)= x^2 - 7}}}

g is the input of f so we replace g(x) with the expression - they are equal

{{{f(g(x))= f(x^2 - 7)}}}

{{{f(x^2 - 7)=(x^2 - 7)^2+7}}}

{{{f(g(x))=(x^2 - 7)*(x^2 - 7)+7}}}

{{{f(g(x))=x^4-14x^2+49+7}}}

{{{f(g(x))=x^4-14x^2+56}}}