**Toolbox:**

- A function $f: X \rightarrow Y$ where for every $x1, x2 \in X, f(x1) = f(x2) \Rightarrow x1 = x2$ is called a one-one or injective function.
- A function$ f : X \rightarrow Y$ is said to be onto or surjective, if every element of Y is the image of some element of X under f, i.e., for every $y \in Y$, there exists an element x in X such that $f(x) = y$.

Given $A=\{1,2,3\} \qquad B=\{4,5,6,7\}$

Step1: Injective or One-One function:

and f is defined by $ f=\{(1,4), (2,5),(3,6)\}$

we see that

$f(1)=4 \qquad f(2)=5 \qquad f(3)=6$

elements 1,2,3 $\in A$ all have district images.

Solution:Therefore $ f=\{(1,4), (2,5),(3,6)\}$ is one-one