Definition, Concept, Example, and evaluation.

Definition: This is the rule which assigns an element x in set A to another unique element y in set B.

Set A is called the Domain while set B is the Co-domain

Image: This is the unique element in set B produced by an element in set A.

Range:  This is the collection of all the images of the elements of the domain.

Using the diagram above:

f(w)= g, f(x)= b, f(y)=f, f(z)=a

a, b, f and g are the images of elements a,b,c and d respectively.

Range = {a, b, f, g,}

The rule which associates each element in set A to a unique element in set B is denoted by any of the following notations: f : A → B or f: A→ B

Example 1: Given f(x) = 3x2 + 2, find the values of (a) f (4)   (b) f (-3) (c) f (-1/2)



F(x) = 3x2+ 2

(a)                F(4), i.e x=4

F(4) = 3(42) + 2 = 3(16) + 2

= 48 + 2

= 50

(b)                F(-3) = 3(-3)2+ 2

= 3(9) +2 = 27 +2

= 29

(c) F(-1/2) = 3(-1/2)2+ 2

= 3(1/4) + 2  = + 2



Example 2: Determine the domain D of the mapping, g:x→ 2x2 – 1, if R= { 1,7,17} is the range  and g is defined on D.


g(x) = 2x2– 1,      R = {1,7,17}

To find the domain, when g(x) = 1,


1.                   Given f(x) = x2+ 4x +3 find the values of.

(a) f(2)    (b) f(½)   (c) f(-3)

2.   Given that f(x) = ax + b and that f(2) = 7 ,f(3) = 12. Find a and b.




One-One mapping: A mapping is one-one if different elements in the domain have different images in the co-domain. If x1= x2 then f(x1) = f(x2)

The mapping is onto and one-one.

NB: In an onto mapping, the range is the same as the co-domain.

Identity Mapping: This is a mapping that takes an element onto itself. If f: x→ x is a mapping such that f(x) = x for all x € X.

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