Least Squares problem with minimize solution

[zollen]

The partial derivatives of [tex]||Ax||^2[/tex] with respect to [tex]x_1......x_n[/tex] fill the vector [tex]2A^TAx[/tex].
The derivatives of [tex]2b^TAx[/tex] fill the vector [tex]2A^Tb[/tex].

So the derivatives of [tex]||Ax - b||^2[/tex] are zero when ______?

My Answer: Ax = b

Am I correct?