Question

Can a linear Equation have $3$ variables ?

Answer 1

The answer is Yes :

Definition of Linear equations : Linear equations are equations of the first order. The linear equations are defined for lines in the coordinate system. When the equation has a homogeneous variable of degree 1 (i.e. only one variable), then it is known as a linear equation in one variable. A linear equation can have more than one variable. If the linear equation has two variables, then it is called linear equations in two variables and so on.

Example of Linear equations of three variables : $x+y+z=0$

Hence the Linear equations can have three variables.