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1.Relation and Function
hard
माना $f:(1,3) \rightarrow R$ एक फलन है, जो $f( x )=\frac{ X [ X ]}{1+ x ^{2}}$, द्वारा परिभाषित है जहाँ $[ x ]$ महत्तम पूर्णाक $\leq x$ को दर्शाता है। तो $f$ का परिसर है
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