Is x = 4 a linear equation with one variable

Is x = 4 a linear equation with one variable

yes
According to - contains only one unknowns, and contains the unknowns of the formula are integral, the degree of the unknowns is 1, such an equation is called unary linear equation
It's like - x = 1, y = 2 are binary linear equations
(believe me, our teachers all teach like this)