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

Bijection Function: – A function is said to be a bijection function if it is one – one as well as onto function.

Now, f : Q → Q, defined by f(x) = x³ + 1

Check for Injectivity:

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

⇒ f(x) = f(y)

⇒ x³ + 1 = y³ + 1

⇒ x³ = y³

⇒ x = y

Hence, f is One – One function

Check for Surjectivity:

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

⇒ x³ + 1 = y

⇒ x³ + 1 – y = 0

Now, we know that for 3 degree equation has a real root

So, let be that root

⇒

⇒

Thus for clearly , there exist such that f(x) = y

Therefore f is onto

Thus, It is a Bijective function