MCQ
Which of the following limits vanish ?

where [ ] denotes greatest integer function

  • A
    $\mathop {Limit}\limits_{x\,\, \to \,\,\infty } {x^{\tfrac{1}{4}}} sin \frac{1}{{\sqrt x }}$
  • B
    $\mathop {Limit}\limits_{x\,\, \to \,\,\pi /2}  (1 - sin x) . tan x$
  • C
    $\mathop {Limit}\limits_{x\,\, \to \,\,{3^ + }} $ $\frac{{{{[x]}^2}\,\, - \,\,9}}{{{x^2}\,\, - \,\,9}}$
  • All of the above

Answer

Correct option: D.
All of the above
d
a) $\lim _{x \rightarrow \infty} x \overline{4} \sin \frac{1}{\sqrt{x}}(0 \times \infty$ form $)$

Rearranging the above expression and using L'Hospital Rule in $\lim _{x \rightarrow \infty}\left(\begin{array}{c}\sin \frac{1}{\sqrt{x}} \\ \frac{-1}{x}\end{array}\right) \Rightarrow \lim _{x \rightarrow \infty}\left(\frac{\cos \frac{1}{\sqrt{x}}\left(\frac{-1}{2}\right) x^{\frac{-3}{2}}}{\left(\frac{-1}{4} x^{\frac{-5}{4}}\right)}=0\right.$

b) $\lim _{x \rightarrow \frac{\pi}{2}}(1-\sin x) \tan x(0 \times \infty$ form $)$

Rearranging and applying L'Hospital Rule $\lim _{x \rightarrow \frac{\pi}{2}} \frac{1-\sin x}{\cot x}=\lim _{x \rightarrow \frac{\pi}{2}} \frac{-\cos x}{-\csc ^{2} x}=\lim _{x \rightarrow \frac{\pi}{2}} \cos x \sin ^{2} x=0$

c) $\lim _{x \rightarrow 3^{+}} \frac{[x]^{2}-9}{x^{2}-9}$

Applying L'Hospital Rule $\left(\frac{0}{0}\right)$ form

The derivative of $[x]$ at $x \rightarrow 3^{+}$ will be 0

Thus, $\lim _{x \rightarrow 3^{+}} \frac{0}{2 x}=0$

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