Distance Detection math for all your isometric or 2.5d needs

http://imgur.com/a/sJ4VJ

Did the math for a project of mine. It was pretty straightforward and fun, but I'd thought I'd share if any one else can benefit.

This isn't a tutorial - I didn't show how to do the math for checking distances. Just have the enemy check (self.x-obj_player.x)^2 + (the same for y)^2 < (agro distance squared)