Tag: continuity

Questions Related to continuity

Number of points of discontinuity of $f\left( x \right) = \left[ {2{x^3} - 5} \right]$ in $\left[ {1,2} \right)$ is where $\left[ x \right]$ denotes greatest integer function are

  1. $14$

  2. $13$

  3. $10$

  4. $8$


Correct Option: A

$f(x)=\displaystyle\lim _{n\rightarrow \infty}\dfrac{(x-1)^{2n}-1}{(x-1)^{2n}+1}$ is discontinuous at

  1. $x=0$ only

  2. $x=2$ only

  3. $x=0$ and $2$

  4. None of these


Correct Option: C

If $f\left( x \right) ={ \left( \tan { \left( \dfrac { \pi  }{ 4 } +\ell nx \right)  }  \right)  }^{ \log _{ x }{ e }  }$ is to be made continuous at $X=1$, then $f(1)$ should be equal to

  1. ${e}^{2}$

  2. $e$

  3. $1/e$

  4. ${e}^{-2}$


Correct Option: B

The function $f\left( x \right)=\left[ x \right] \cos { \left( \pi \left( \dfrac { 2x-1 }{ 2 }  \right)  \right)  } $. (where [.] denotes the greatest integer function ) is discontinuous.  

  1. For each real $x$

  2. For each integral point

  3. No where

  4. At each non-integral point


Correct Option: A

If $f(x)=\dfrac {1}{x^{2}-17x+66}$ then $f\left(\dfrac {2}{x-2}\right)$ is discontinuous at $x=$

  1. $2,\dfrac {7}{3},\dfrac {25}{11}$

  2. $2,\dfrac {7}{3},\dfrac {24}{11}$

  3. $2,\dfrac {8}{3},\dfrac {24}{11}$

  4. $None\ of\ these$


Correct Option: A

The sum of all values of $x$ for which $f(x)=[3\sin x]$ is discontinous in $[0,\ 2\pi]$ is (where [.] represents greatest integers function)

  1. $\dfrac {21\pi}{2}$

  2. $13\ \pi$

  3. $11\ \pi$

  4. $\dfrac {23\pi}{2}$


Correct Option: B

Consider the function defined on $[0,\ 1]\rightarrow R,\ f(x)=\dfrac {\sin x-x\cos x}{x^{2}}$ if $x\neq 0$ and $f(0)=0$ then the function of $f(x)$. 

  1. Has a removable discontinuity at $x=0$

  2. Has a removable finite discontinuity at $x=0$

  3. Has a non removable infinite discontinuity at $x=0$

  4. Is continuous at $x=0$


Correct Option: A

The function $f(x)={ sin }^{ -1 }(cosx)$ is :

  1. Discontinuous at x = 0

  2. Continuous at x = 0

  3. Differentiable at x = 0

  4. None of these


Correct Option: A
Explanation:

$f(x)=\sin^{-1} (\cos x)$

LHL :
$lim _{x\rightarrow 0^-} \sin^{-1}(\cos x)=lim _{h\rightarrow 0} \sin^{-1}(\cos (0-h))$

$lim _{h\rightarrow 0} \sin^{-1} (\cos (-h))=lim _{h\rightarrow 0} \sin^{-1}(\cos 0)=\dfrac{\pi}{2}$

RHL:
$lim _{x\rightarrow 0^{+}} \sin^{-1}(\cos x)$
$=lim _{h\rightarrow 0} \sin^{-1} \cos (0+h)$
$=\sin^{-1} \cos 0$
$=\dfrac{\pi}{2}$

Thus, $LHL=RHL=f(0)=\dfrac{\pi}{2}$

RHD :
$lim _{h\rightarrow 0}\dfrac{f(x+h)-f(x)}{h}=\dfrac{sin^{-1}(\cos h)-1}{h}$

$lim _{h\rightarrow 0} \dfrac{\sin^{-1}(\cos h)-1}{h}=\dfrac{1-\sin h}{\sqrt{1-\cos^2 h}}=\dfrac{-\sin h}{\sin h}=-1$

LHD :
$lim _{h\rightarrow 0} \dfrac{f(x-h)-f(x)}{-h}=lim _{h\rightarrow 0}\dfrac{\sin^{-1}(\cos -h)-1}{-h}$

$lim _{h\rightarrow 0} \dfrac{\sin^{-1}(\cos h)-1}{-h}=\dfrac{-\sin h}{-\sin h}=1$

$LHD \neq RHD$
Thus, function is not differentiable at $x=0$.

If $f\left( x \right) =\begin{cases} -1,if\ x<0\ \ 0,if\ x=0\ \ 1,if\ x>0\ \end{cases}$ and $g\left(x\right)=\sin x +\cos x$, then point discontinuity of $(fog)(x)$ in $(0,2\pi)$ are 

  1. $\dfrac{\pi}{4},\dfrac{5\pi}{4}$

  2. $\dfrac{\pi}{4},\dfrac{3\pi}{4}$

  3. $\dfrac{\pi}{4},\dfrac{7\pi}{4}$

  4. $\dfrac{3\pi}{4},\dfrac{7\pi}{4}$


Correct Option: A

$f(x)=\min { \left{ x,{ x }^{ 2 } \right} ,\forall x\epsilon R } $ then $f(x)$ is 

  1. discontinuous at $0$

  2. discontinuous at $1$

  3. continuous on $R$

  4. continuous on $0,1$


Correct Option: A