Linear equation with one variable can be put in the form:
\begin{align} ax&=b \Rightarrow\\ \\ x&=\frac{b}{a},\; \textrm{kui}\; a\neq 0\\ \end{align}
where,
x— variable, unknown;
a, b— coefficient, constant.
Linear equation with two variables can be put in the form:
ar \begin{align} y=ax+b\\ \end{align}
A linear equation with two variables is an equation whose solutions form a line - thus linear equation.
Linear equation with more than two variables may be put in the form:
\begin{align} a_{1}x_{1}+a_{n}x_{n}+b=0\\ \end{align}
If we have more than one equations involving the same set of variables, they form a system of linear equations.