I have the exact same question as this :Sum of projections
This was asked in 2011- I have asked my own question about it in the comments (you can see the comments) but sadly the original asker is happy and understands the solution unlike me- How do I "reawaken" the question so that somebody who posted in the thread replies- no new person will reply because it won't appear as a new question- it's been resolved- and many users who discussed it then at the time have not been seen on stackeexchange for months or years.
In general what do I do for future questions when a situation like this arises?