Chapter 2.5, Problem 3E

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.

3. $A=\left[\begin{array}{ccc}2& -1& 2\\ -6& 0& 7\\ 8& -1& 5\end{array}\right],b=\left[\begin{array}{c}1\\ 0\\ 4\end{array}\right]$

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