THIS IS WRONG.

I have my further idea, but I am not sure whether it is correct.

From , since

,

it should be clear that \frac{\partial f_1}{\partial x_j}(c))^2 + .. +(\frac{\partial f_n}{\partial x_j}(c))^2 = q_j [/tex] for any and

Hence I could write

I think there should have to be some way to reason from the above that

? ? ?