A *m × n* system of linear equations with *m < n*
is overdetermined. There are more equations than there are
unknowns. “Solving” this equation is the process
of reducing the system to an *m × m* problem then
solving the reduced set of equations. A common technique for
constructing a reduced set of equations is known as the least
squares solution to the equations. The least squares equations
are derived by premultiplying
Equation 35
by **A ^{T}**, i.e.

$$\mathbf{\left({A}^{T}A\right)x={A}^{T}b}$$ | (42) |

Often Equation 42 is referred to as the normal equations of the linear least squares problem. The least squares terminology refers to the fact that the solution to Equation 42 minimizes the sum of the squares of the differences between the left and right sides of Equation 35.