Chapter 13 Linear Equations and Matrices

13.1 Examples of systems of linear equations

        Suppose a system of linear equations is:

\begin{cases}2x-5y=7\\-2x+4y=-6\end{cases}

        Converted to matrix form:

 \begin{bmatrix}2&-5\\-2&4\end{bmatrix}\;\begin{bmatrix}x\\y\end{bmatrix}=\begin{bmatrix}7\\-6\end{bmatrix}\

        Assumptions:

A=\begin{bmatrix}2&-5\\-2&4\end{bmatrix}\;\vec{x}=\begin{bmatrix}x\\y\end{bmatrix}\;\vec{b}=\begin{bmatrix}7\\-6\end{bmatrix}\

        The above equation becomes: 

A\vec{x}=\vec{b}

A^{-1}A\vec{x}=A^{-1}b

 \vec{x}=A^{-1}b

        Assumptions:

 A = \begin{bmatrix}a&b\\c&d\end{bmatrix}\

        Its inverse matrix is:

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