Answer
$(F-G)(x)=F(x)-G(x)\,\,\,\,\,\,by\,definition\,of\,(F-G)(x)\\
(F-G)(x)=F(x)-G(x)=-(G(x)-F(x))=-(G-F)(x)\\
by\,definition\,of\,(G-F)(x)\\
\because (F-G)(x)=-(G-F)(x)\\
\therefore F-G\neq G-F\\
$
Work Step by Step
$(F-G)(x)=F(x)-G(x)\,\,\,\,\,\,by\,definition\,of\,(F-G)(x)\\
(F-G)(x)=F(x)-G(x)=-(G(x)-F(x))=-(G-F)(x)\\
by\,definition\,of\,(G-F)(x)\\
\because (F-G)(x)=-(G-F)(x)\\
\therefore F-G\neq G-F\\
$