Question

This problem uses least squares to find the curve \(y=a x+b x^{2}\) that best fits these 4 points in the plane:

$$ \left(x_{1}, y_{1}\right)=(-2,2), \quad\left(x_{2}, y_{2}\right)=(-1,1), \quad\left(x_{1}, y_{3}\right)=(1,0), \quad\left(x_{4}, y_{4}\right)=(2,2) . $$

a. Write down 4 equations \(a x_{i}+b x_{i}^{2}=y_{i}, i=1,2,3,4\), that would be true if the line actually went through a11 four points.

b. Now write those four equations in the form \(\mathbf{A}\left[\begin{array}{l}a \\ b\end{array}\right]=\mathbf{y}\)

c. Now find \(\left[\begin{array}{l}\hat{a} \\ \hat{b}\end{array}\right]\) that minimizes \(\left\|A\left[\begin{array}{l}a \\ b\end{array}\right]-\mathbf{y}\right\|^{2}\).

Answer 1