1.Relation and Function
hard

Let $f:(1,3) \rightarrow \mathrm{R}$ be a function defined by

$f(\mathrm{x})=\frac{\mathrm{x}[\mathrm{x}]}{1+\mathrm{x}^{2}},$ where $[\mathrm{x}]$ denotes the greatest

integer $\leq \mathrm{x} .$ Then the range of $f$ is

A

$\left(\frac{3}{5}, \frac{4}{5}\right)$

B

$\left(\frac{2}{5}, \frac{3}{5}\right] \cup\left(\frac{3}{4}, \frac{4}{5}\right)$

C

$\left(\frac{2}{5}, \frac{4}{5}\right]$

D

$\left(\frac{2}{5}, \frac{1}{2}\right) \cup\left(\frac{3}{5}, \frac{4}{5}\right]$

(JEE MAIN-2020)

Solution

$f(\mathrm{x})=\left\{\begin{array}{ll}{\frac{\mathrm{x}}{\mathrm{x}^{2}+1}} & {; \quad \mathrm{x} \in(1,2)} \\ {\frac{2 \mathrm{x}}{\mathrm{x}^{2}+1}} & {; \quad \mathrm{x} \in[2,3)}\end{array}\right.$

$f(\mathrm{x})$ is decreasing function

$f(x) \in\left(\frac{2}{5}, \frac{1}{2}\right) \cup\left(\frac{3}{5}, \frac{4}{5}\right]$

Standard 12
Mathematics

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