Q. 1 A3.8( 17 Votes )

# Give an example of a functionWhich is one – one but not onto.

TIP: One – One Function: – A function is said to be a one – one functions or an injection if different elements of A have different images in B.

So, is One – One function

a≠b

f(a)≠f(b) for all

f(a) = f(b)

a = b for all

Onto Function: – A function is said to be a onto function or surjection if every element of A i.e, if f(A) = B or range of f is the co – domain of f.

So, is Surjection iff for each , there exists such that f(a) = b

Now, Let, given by f(x) = x2

Check for Injectivity:

Let x,y be elements belongs to N i.e such that

So, from definition

f(x) = f(y)

x2 = y2

x2 – y2 = 0

(x – y)(x + y) = 0

As therefore x + y>0

x – y = 0

x = y

Hence f is One – One function

Check for Surjectivity:

Let y be element belongs to N i.e be arbitrary, then

f(x) = y

x2 = y

not belongs to N for non–perfect square value of y.

Therefore no non – perfect square value of y has a pre image in domain N.

Hence, given by f(x) = x2 is One – One but not onto.

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