Show that the function is a one-to-one correspondence.
$f: \mathbb{R} \to \mathbb{R}$ given by $f(x) = mx + b$, $m \ne 0$
Proof.
i. Suppose $x, y \in \mathbb{R}$ and $f(x) = f(y)$. Then $mx + b = my + b$, so $mx = my$. Because $m \ne 0$, we have $x = y$. Therefore $f$ is one-to-one.
ii. Let $z \in \mathbb{R}$. Choose $t = \frac{z - b}{m}$. Because $m \ne 0$, $t \in \mathbb{R}$. Then $f(t) = m(\frac{z - b}{m}) + b = z$. Therefore, $f$ is onto $\mathbb{R}$.