+501 If $f(x)=f(2-x)$ for all $x$, then what line is necessarily an axis of symmetry of the graph of $y=f(x)$? (Give the simplest equation of this line.)
+600
We claim that it's $\boxed{x=1}$.
Notice that $f(1)=f(1)$, and $f(1+k)=f(1-k)$, implying the answer.
