Question

Given f(x) = 2x and g(x) = x2+3 , find f(g(x)).

Answer 1

I'm assuming for g(x) you mean g(x) = x^2+3 for $g(x)=x^2+3$.

Going with that...

    $\begin{aligned}f(g(x)) &= f\left( x^2+3 \right)~~~~~\text{plug x^2+3 in for x in f(x) }\\[0.5em]&= 2\cdot ( x^2+3 )~~~~~\text{so 2x became 2(x^2+3) }\\[0.5em]&= 2x^2+6\endaligned}$

Just treat the enter g(x) function as a single input for f(x).