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JEE MAIN 2019
09-01-19 S2
Question
Let $A=\{x \in R: x$ is not a positive integer $\}$. Define a function $f: A \rightarrow R$ as $f(x)=\frac{2 x}{x-1}$, then $f$ is
Select the correct option:
A
Injective but not surjective
B
Neither injective nor surjective
C
Surjective but not injective
D
Not injective
✓ Correct! Well done.
✗ Incorrect. Try again or view the solution.
Solution
As $A=\{x \in R: x$ is not a positive integer $\}$ $f: A \rightarrow R$ given by $f(x)=\frac{2 x}{x-1}$ $$ f\left(x_1\right)=f\left(x_2\right) \Leftrightarrow x_1=x_2 $$ So, $f$ is one-one. As $\mathrm{f}(\mathrm{x}) \neq 2$ for any $\mathrm{x} \in \mathrm{A} \Rightarrow \mathrm{f}$ is not onto. $\therefore \mathrm{f}$ is injective but not surjective.
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