An equation in one variable can be easily represented on a number line by plotting the value of the variable on it. We can also represent the equation on a graph by considering the coefficient of the missing variable as zero, and then assuming the different values of the missing variable we can find the solutions and then plot the solutions on the graph.
Illustration: Plot the equation x= 4 on the graph
Solution: Let the coefficient of the missing variable be zero. The equation can be written as ; x + 0y = 4
For y=2 , the equation becomes x + 0(2)=4 or x = 4
For y=4 , the equation becomes x + 0(4)=4 or x = 4
For y=6 , the equation becomes x + 0(6)=4 or x = 4
So (4,2), (4,4) and (4,6) are the solution of the equation plotting them on the graph we get
We get a line parallel to Y- Axis
Similarly if we plot the equation y=4, we get a line parallel to X- Axis
We can further generalize that an equation in one variable represents a line parallel to the axis whose variable is missing in the equation.