I am supposed to work outhttp://s3.amazonaws.com/answer-board...0825008079.gif to show that it has a solution where x minimizes http://s3.amazonaws.com/answer-board...6450004174.gif. I guess my question is where to even begin. When I do the block matrix multiplication, I get:

http://s3.amazonaws.com/answer-board...9575001171.gif

Which tells me r + Ax = b and A*r = 0... but I don't know how to complete it or bring in the minimization?