Question

Let $A=\left\{1,2,3,4\right\}$ and $R$ is a relation on $A$ such that $R=\left\{\left(a,b\right):a=2b\right\}$

Answer 1

Consider, $A=\left\{1,2,3,4\right\},R=\left\{\left(a,b\right):a=2b\right\}$
$\begin{array}{c}B=2\times 1,2\times 2,2\times 3,2\times 4\\ =\left\{2,4,6,8\right\}\end{array}$
and if $R:A\to \left\{1,2\right\}\to \left\{2,4\right\}$