Chapter 2.5, Problem 6E

In Exercises 1–6, solve the equation Ax = b by using the LU factorization given for A. In Exercises 1 and 2, also solve Ax = b by ordinary row reduction.

6. $A=\left[\begin{array}{cccc}1& 3& 4& 0\\ -3& -6& -7& 2\\ 3& 3& 0& -4\\ -5& -3& 2& 9\end{array}\right],b=\left[\begin{array}{c}1\\ -2\\ -1\\ 2\end{array}\right]$

$A=\left[\begin{array}{cccc}1& 0& 0& 0\\ -3& 1& 0& 0\\ 3& -2& 1& 0\\ -5& 4& -1& 1\end{array}\right]\left[\begin{array}{cccc}1& 3& 4& 0\\ 0& 3& 5& 2\\ 0& 0& -2& 0\\ 0& 0& 0& 1\end{array}\right]$