Show that each orientation-reversing isometry has the form
$\bar f(z)=c+e^{i\theta}\bar z$, which becomes
$\bar g(z)=ce^{-i(\theta/2)}+\bar z$ after rotation of axes and
$\bar h(z)==\alpha+\bar z$, where $\alpha \in \mathbb R$, after translation of O.
I don't understand even where to start, I don't understand orientation-reversaing isometries, and I don't understand the significance of "$==$"