ANSWER :
(f - g)(x) = x^2 + 8
EXPLANATION :
From the problem, we have :
[tex]\begin{gathered} f(x)=2x^2+1 \\ g(x)=x^2-7 \end{gathered}[/tex](f - g)(x) is the difference between the two functions
That will be :
[tex]\begin{gathered} (f-g)(x)=f(x)-g(x) \\ =2x^2+1-(x^2-7) \\ =2x^2+1-x^2+7 \\ =x^2+8 \end{gathered}[/tex]