[Alter Kaker]

Isn’t the territory controlled by ISIS in Libya on the far side from Egypt??

No, it's mostly on the side close to Egypt. However the beheadings apparently took place near Tripoli on the far side. In any event, Egyptian planes can hit targets pretty much anywhere in Libya.

[GeronL]

The map I saw on Wiki showed Derna or Durna on the far side, or maybe I was cross-eyed when I looked at it.