This is the image of $|y|=F(x)$ , here the dotted part was the part of the original F(x) is the part that was cut off.
$$ y = \begin{cases} F(x), & \text{if $F(x) \ge 0$} \\ -F(x), & \text{if $F(x) < 0$} \end{cases} $$
if we use this then I afraid we get the wrong graph :?
Our graph in that case would like this :
I am sorry if it is a silly doubt (Maybe am making a silly mistake :/
) !