For a point , the functional value is called the image of the point s. If , then the set of the images of elements of is called the image of and denoted by .Thus
Clearly,
Suppose .The set is called the inverse image of under and is denoted by .
Example 1Suppose and is defined by and . Therefore,
, the functional value is called the image of the point 
, then the set of the images of elements of 
is called the image of 
.Thus 
.The set 
is called the inverse image of 
under 
and is denoted by 
.
and 
is defined by 
and 
. Therefore,
is 1 and that of 
is -1.