Mik's Least Squares Derivation
May 11, 1987

Let X  be defined to be:
 X .
Then we wish to compute:
X
and
X .
By the chain rule for differentiation, we have:
X ,  and  X ,

hence since X  is 

X ,

 and  X  is

X ,
we have:
X  is X

X  is X