The relation R is defined on the set of natural numbers as $\{(a,b):a=2b\}$. Then $R^{-1}$ is given by:

{(2, 1), (4, 2), (6, 3). . . . } {(1, 2), (2, 4), (3, 6). . . . } $R^{-1}$ is not defined None of these

{(1, 2), (2, 4), (3, 6). . . . }

$R=\{(2,1)(4,2)(6,3),......\}$. So $R^{-1}=\{(1, 2), (2, 4), (3, 6). . . . \}$