Question-1 :-  Give the geometric representations of y = 3 as an equation
(i) in one variable
(ii) in two variables

(i) In one variable, y = 3 represents a point as shown in following figure.
    
    

(ii) In two variables, y = 3 represents a straight line passing through point (0, 3) and parallel to x-axis. 
  It is a collection of all points of the plane, having their y-coordinate as 3.   
    
    

Question-2 :-  Give the geometric representations of 2x + 9 = 0 as an equation
(i) in one variable
(ii) in two variables

(i) In one variable, 2x + 9 = 0 represents a point x = -9/2 = -4.5 as shown in the following figure.    
    
(ii) In two variables, 2x + 9 = 0 represents a straight line passing through point (-4.5, 0) and parallel to y-axis.
  It is a collection of all points of the plane, having their x-coordinate as 4.5.