Fit an equation to a matrix

Hi all,

I have a matrix like 

       a=[3 7 6; 8 5 7; 1 4 7]; 

I want to fit an equation like  below to all elements of a matrix.
how can I write this program 

          y= -5E-05*X^2 + 0.115*X + 1989.6, 

Thanks in advance

[José-Luis]

What is x and what is y in that matrix?

 doc fit