Lets suppose that \(\displaystyle f(x)=1-x\).
\(\displaystyle f(4)=-3\) Do you have any doubt whatsoever about that? If you do please post it.
\(\displaystyle f(-4)=5\) Do you have any doubt whatsoever about that? If you do please post it.
Now suppose that \(\displaystyle g(x)=-x\)
\(\displaystyle g(4)=-4\) Do you have any doubt whatsoever about that? If you do please post it.
\(\displaystyle g(-4)=-(-4)=4\) Do you have any doubt whatsoever about that? If you do please post it.
Now suppose that \(\displaystyle h(x)=|x|\)
\(\displaystyle h(4)=4\) Do you have any doubt whatsoever about that? If you do please post it.
\(\displaystyle h(-4)=4\) Do you have any doubt whatsoever about that? If you do please post it.