Give the geometric representations of 2x + 9 = 0 as an equation 

(i) in one variable 

(ii) in two variables

(i) 2x + 9 = 0
We have, 2x + 9 = 0 

⇒ 2x = – 9 

⇒ x = −$\frac{9}{2}$

which is a linear equation in one variable i.e., x only.
 x = −$\frac{9}{2}$ is a unique solution and it is shown on number line below:
 

(ii) 2x +9=0

We can write 2x + 9 = 0 in two variables as 2x + 0y + 9 = 0

or $x=\frac{-9-0y}{2}$
∴ For y = 1, $x=\frac{-9-0\times 1}{2}$ = −$\frac{9}{2}$

∴ For y = 2, $x=\frac{-9-0\times 2}{2}$ = −$\frac{9}{2}$

∴ For y = 3, $x=\frac{-9-0\times 3}{2}$ = −$\frac{9}{2}$
 

Now, on plotting the points (−$\frac{9}{2}$,1) ,(−$\frac{9}{2}$,2) and (−$\frac{9}{2}$,3) on a graph paper and joining them, we get a line PQ as solution of 2x + 9 = 0.