Q. If $\left\lbrack \cot^{- 1}x \right\rbrack + \left\lbrack \cos^{- 1}x \right\rbrack = 0,\$where $x$ is a non-negative real number and [.] denotes the greatest integer function, then complete set of values of $x$ is

A) $(\cos{1,1}\rbrack$
B) $(\cot{1,1})$
C) $(\cos{1,\cot 1})$
D) None of these
Explanation

(b)
$\because 0 \leq \cos^{- 1}{x \leq \pi}$
And $0 < \cot^{- 1}{x < \pi}$
Given, $\lbrack\cot^{- 1}{x\rbrack + \lbrack\cot^{- 1}{x\rbrack = 0}}$
$\Rightarrow \lbrack\cot^{- 1}{x\rbrack = 0\ and\ \lbrack\cos^{- 1}{x\rbrack = 0}}$
$\Rightarrow 0 < \cot^{- 1}{x < 1\ and\ 0 \leq \cos^{- 1}{x < 1}}$
$\therefore x \in (\cot{1,\infty)\ and\ x \in (\cos{1,\ 1)}}$
$\Rightarrow x \in (\cot{1,\ 1})$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.