Optimizing the above equation, that is
∇f=0=Ax−b,which leads to a simple matrix-inversion problem
x=A−1b.This problem is easy to solve since we can calculate the inverse. Alternatively, we can solve the two coupled equations with two unknowns
∂f∂x1=2x1+x2−5=0,and
∂f∂x2=x1+20x2−3=0,with solutions x1=97/39 and x2=1/39.