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--- lecture_4_slides [2017/02/01 17:16] – [Reduced row echelon form (RREF)] rupert
+++ lecture_4_slides [2017/02/01 17:19] (current) – [Example] rupert
@@ Line 95: / Line 95: @@
   * e.g. $\left[\begin{smallmatrix} {\color{blue}1}&{\color{red}2}&{\color{red}3}&4&5\\0&{\color{blue}1}&{\color{red}2}&3&4\\0&0&{\color{blue}1}&2&3\end{smallmatrix}\right]$ and $\left[\begin{smallmatrix} {\color{blue}1}&0&{\color{red}3}&4&5\\0&{\color{blue}1}&0&3&4\\0&0&{\color{blue}1}&2&3\end{smallmatrix}\right]$ are in REF but not RREF
   * e.g. $\left[\begin{smallmatrix} {\color{blue}1}&0&0&4&5\\0&{\color{blue}1}&0&3&4\\0&0&{\color{blue}1}&2&3\end{smallmatrix}\right]$ is in RREF.
-  * What about $\left[\begin{smallmatrix} {\color{blue}1}&9&0&4&5\\0&0&{\color{blue}1}&0&3\\0&0&0&{\color{blue}1}&2\end{smallmatrix}\right]$ and $\left[\begin{smallmatrix} {\color{blue}1}&9&0&0&5\\0&0&{\color{blue}1}&0&3\\0&0&0&{\color{blue}1}&2\end{smallmatrix}\right]$?
+  * How about $\left[\begin{smallmatrix} {\color{blue}1}&9&0&4&5\\0&0&{\color{blue}1}&0&3\\0&0&0&{\color{blue}1}&2\end{smallmatrix}\right]$, $\left[\begin{smallmatrix} {\color{blue}1}&9&0&0&5\\0&0&{\color{blue}1}&0&3\\0&0&0&{\color{blue}1}&2\end{smallmatrix}\right]$, $\left[\begin{smallmatrix} {\color{blue}1}&0&0&0&5\\0&0&{\color{blue}1}&0&3\\0&0&0&{\color{blue}1}&2\end{smallmatrix}\right]$?
 ==== Example ====
@@ Line 144: / Line 144: @@
     * $ x_1+2x_2+3x_3=8\implies x_1=5-2s-6t.$
   * So $ \left[\begin{smallmatrix} x_1\\x_2\\x_3\\x_4 \\x_5\end{smallmatrix}\right]= \left[\begin{smallmatrix} 5\\0\\1\\4\\0\end{smallmatrix}\right] +s\left[\begin{smallmatrix} -2\\1\\0\\0\\0\end{smallmatrix}\right] +t\left[\begin{smallmatrix} -6\\0\\2\\-3\\1\end{smallmatrix}\right],\quad s,t\in \mathbb{R}.$
-  * (A $2$-dimensional set in $5$-dimensional space $\mathbb{R}^5$).
+  * 2 free vars, 5 vars in all
+  * Solution set is $2$-dimensional, in $5$-dimensional space $\mathbb{R}^5$.