The way you posted this makes very difficult to read.
If we know that is a parallelogram then
Based on this diagram http://i55.tinypic.com/2w4wtio.jpg , what is the sum of: ->AB + ->ED + ->CA. Since they have to go head to tail and ED=BC would it be AB + BC + CA? This does not look right to me.
I hope I posted this in the correct forum and I apologize if I did not. Thanks.