Question

If $B$ is the set of even positive integers then $f:N\to B$ defined by $f\left(x\right)=2x$ is

• A. one - one only
• B. onto only
• C. neither one-one nor onto
• D. bijective

Answer 1

The correct option is D bijective

$f\left(x\right)$ is monotonic & every monotonic function is one - one & range of $f\left(x\right)=$ codomain
$\therefore f\left(x\right)$ is onto.
And a function which is both one - one & onto is called bijective.