Answer
$F(x)=f\circ g(x)$ for
$g(x)=\cos x,\qquad f(x)=x^{2}$
Work Step by Step
$f\circ g(x)=f[g(x)]$
Rule of thumb: Ask yourself
what would be the last operation if you used a calculator, step by step?
(Answer: Square the current result)
$f(x)=x^{2}$
$ F(x)=f(\cos x)$
So, if
$g(x)=\cos x$ and $f(x)=x^{2}$
then
$F(x)=f\circ g(x)$