diff --git a/Chapters/chapter3.tex b/Chapters/chapter3.tex index 836249d..1df64e5 100644 --- a/Chapters/chapter3.tex +++ b/Chapters/chapter3.tex @@ -1419,11 +1419,15 @@ \subsection{Problems} \label{2009_a5_2} Consider the following 4 dimensional vectors $\aa_1$, $\aa_2$, and $\aa_3$ such that $$ -a_1 = \left[\begin{array}{c} 1\\1\\0\\0 \end{array}\right] \qquad -a_2 = \left[\begin{array}{c} 0\\0\\4\\-3 \end{array}\right] \qquad -a_3 = \left[\begin{array}{c} 10\\0\\-5\\0 \end{array}\right] +\aa_1 = \left[\begin{array}{c} 1\\1\\0\\0 \end{array}\right] \qquad +\aa_2 = \left[\begin{array}{c} 0\\0\\4\\-3 \end{array}\right] \qquad +\aa_3 = \left[\begin{array}{c} 10\\0\\-5\\0 \end{array}\right] +$$ +Are these linearly independent? Can the vector ${\bf y}$ below be written as a +linear combination of the above three vectors? +$$ +{\bf y} = \left[\begin{array}{c} 11\\1\\-1\\10 \end{array}\right] $$ -Are these linearly independent? Can the vector $\boldmath{y}$ below be written as linear combination of the above three vectors? \end{problem} @@ -3078,9 +3082,9 @@ \section{Solutions to Chapter Problems} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \vspace{2mm} \noindent {\bf Solution \ref{2009_a5_2}} -The vectors $a_1$, $a_2$, and $a_3$ are linearly independent if the only solution to the system +The vectors $\aa_1$, $\aa_2$, and $\aa_3$ are linearly independent if the only solution to the system $$ -x_1a_1 + x_2a_2 + x_3a_3 = 0 +x_1\aa_1 + x_2\aa_2 + x_3\aa_3 = 0 $$ is $x_1=x_2=x_3=0$ So, @@ -3094,14 +3098,17 @@ \section{Solutions to Chapter Problems} \end{eqnarray*} The system has a unique solution $x_1=x_2=x_3=0$, hence the three vectors are linearly independent. -To find if $y$ can be written as a linear combination of the three vectors, we look for a solution of the system +To find if ${\bf y}$ can be written as a linear combination of the three vectors, we look for a solution of the system \begin{eqnarray*} &&\left[\begin{array}{ccc|c}1&0&10&11 \\ 1&0&0&1 \\ 0&4&-5&-1 \\ 0&-3&0&10\end{array}\right]\rarr \begin{array}{c}(2,:)=(2,:)-(1,:)\\(3,:)=(3,:)+(4,:)\end{array}\rarr \left[\begin{array}{ccc|c}1&0&10&11 \\ 0&0&-10&-10 \\ 0&1&-5&9 \\ 0&-3&0&10\end{array}\right]\rarr\\ &&\begin{array}{c}(2,:)=-\frac{1}{10}(2,:)\\(4,:)=(4,:)+3(3,:)\end{array}\rarr \left[\begin{array}{ccc|c}1&0&10&11 \\ 0&0&1&1 \\ 0&1&-5&9 \\ 0&0&-15&37\end{array}\right] \end{eqnarray*} -The second row of the reduced row echelon matrix implies that $x_3=1$, while the third row yields that $x_3 = -\frac{37}{15}$. This contradiction means that the system has no solution, and $y$ is therefore not a linear combination of $a_1$, $a_2$, and $a_3$. +The second row of the reduced row echelon matrix implies that $x_3=1$, +while the third row yields that $x_3 = -\frac{37}{15}$. This contradiction +means that the system has no solution, and ${\bf y}$ is therefore not a +linear combination of $\aa_1$, $\aa_2$, and $\aa_3$. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \vspace{2mm}