System of linear equations/Set of variables/Homogeneous and inhomogeneous/Definition

System of linear equations

Let ${}K$ denote a field, and let ${}a_{ij}\in K$ for ${}1\leq i\leq m$ and ${}1\leq j\leq n$. We call

${\begin{matrix}a_{11}x_{1}+a_{12}x_{2}+\cdots +a_{1n}x_{n}&=&0\\a_{21}x_{1}+a_{22}x_{2}+\cdots +a_{2n}x_{n}&=&0\\\vdots &\vdots &\vdots \\a_{m1}x_{1}+a_{m2}x_{2}+\cdots +a_{mn}x_{n}&=&0\end{matrix}}$

a (homogeneous) system of linear equations in the variables ${}x_{1},\ldots ,x_{n}$. A tuple ${}(\xi _{1},\ldots ,\xi _{n})\in K^{n}$ is called a solution of the linear system if ${}\sum _{j=1}^{n}a_{ij}\xi _{j}=0$ holds for all ${}i=1,\ldots ,m$.

If ${}(c_{1},\ldots ,c_{m})\in K^{m}$ is given, then

${\begin{matrix}a_{11}x_{1}+a_{12}x_{2}+\cdots +a_{1n}x_{n}&=&c_{1}\\a_{21}x_{1}+a_{22}x_{2}+\cdots +a_{2n}x_{n}&=&c_{2}\\\vdots &\vdots &\vdots \\a_{m1}x_{1}+a_{m2}x_{2}+\cdots +a_{mn}x_{n}&=&c_{m}\end{matrix}}$

is called an inhomogeneous system of linear equations. A tuple ${}(\zeta _{1},\ldots ,\zeta _{n})\in K^{n}$ is called a solution to the inhomogeneous linear system if ${}\sum _{j=1}^{n}a_{ij}\zeta _{j}=c_{i}$ holds for all ${}i$.