One of these is left and another is right but I forget which. But if you know how to use front and back already I'm sure you can figure it out.
The only different is instead of two minus signs or two plus signs you go with one of each.
[(getpos _unit select 0) + (sin getdir _unit*_number),(getpos _unit select 1) - (cos getdir _unit*_number),0]
[(getpos _unit select 0) - (sin getdir _unit*_number),(getpos _unit select 1) + (cos getdir _unit*_number),0]