Chapter 6.5, Problem 16E

In Exercises 15 and 16, use the factorization A = QR to find the least-squares solution of Ax = b.

16. A = $\left[\begin{array}{cc}1& -1\\ 1& 4\\ 1& -1\\ 1& 4\end{array}\right]=\left[\begin{array}{cc}1/2& -1/2\\ 1/2& 1/2\\ 1/2& -1/2\\ 1/2& 1/2\end{array}\right]\left[\begin{array}{cc}2& 3\\ 0& 5\end{array}\right]$, b = $\left[\begin{array}{c}-1\\ 6\\ 5\\ 7\end{array}\right]$