Let the sets A and B denote the domain and range respectively of the function $f(x)=\frac{1}{\sqrt{\lceil x\rceil-x}}$, where $\lceil x\rceil$ denotes the smallest integer greater than or equal to $x$. Then among the statements
(S1) : $A \cap B=(1, \infty)-\mathbb{N}$ and
(S2) : $A \cup B=(1, \infty)$
Solution
$f(x)=\frac{1}{\sqrt{\lceil x\rceil-x}}$
<br/><br/>If $\mathrm{x} \in \mathrm{I},\lceil\mathrm{x}\rceil=[\mathrm{x}]$ (greatest integer function)
<br/><br/>If $x \notin I,\lceil x\rceil=[x]+1$
<br/><br/>$$
\begin{aligned}
& \Rightarrow \mathrm{f}(\mathrm{x})=\left\{\begin{array}{l}
\frac{1}{\sqrt{[\mathrm{x}]-\mathrm{x}}}, \mathrm{x} \in \mathrm{I} \\\\
\frac{1}{\sqrt{[\mathrm{x}]+1-\mathrm{x}}}, \mathrm{x} \notin \mathrm{I}
\end{array}\right. \\\\
& \Rightarrow \mathrm{f}(\mathrm{x})=\left\{\begin{array}{l}
\frac{1}{\sqrt{-\{\mathrm{x}\}}}, \mathrm{x} \in \mathrm{I}, \text { (does not exist) } \\\\
\frac{1}{\sqrt{1-\{\mathrm{x}\}}}, \mathrm{x} \notin \mathrm{I}
\end{array}\right. \\\\
& \Rightarrow \text { domain of } \mathrm{f}(\mathrm{x})=\mathrm{R}-\mathrm{I}
\end{aligned}
$$
<br/><br/>$$
\begin{aligned}
& \text { Now, } \mathrm{f}(\mathrm{x})=\frac{1}{\sqrt{1-\{\mathrm{x}\}}}, \mathrm{x} \notin \mathrm{I} \\\\
& \Rightarrow 0<\{\mathrm{x}\}<1 \\\\
& \Rightarrow 0<\sqrt{1-\{\mathrm{x}\}}<1 \\\\
& \Rightarrow \frac{1}{\sqrt{1-\{\mathrm{x}\}}}>1 \\\\
& \Rightarrow \text { Range }=(1, \infty) \\\\
& \Rightarrow \mathrm{A}=\mathrm{R}-\mathrm{I}
\end{aligned}
$$
<br/><br/>$$
\begin{aligned}
& B=(1, \infty) \\\\
& \text { So, } A \cap B=(1, \infty)-N \\\\
& A \cup B \neq(1, \infty) \\\\
& \Rightarrow S 1 \text { is only correct }
\end{aligned}
$$
About this question
Subject: Mathematics · Chapter: Sets, Relations and Functions · Topic: Sets and Operations
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