Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Continuity and Differentiability

Question:

Statement - 1: Let $f(x)=[3+4 \sin x]$, where [.] denotes the greatest integer function. The number of discontinuities of $f(x)$ in $[\pi, 2 \pi]$ is 6.

Statement - 2: The range of $f$ is $\{-1,0,1,2,3\}$.

Options:

Statement-1 is True, Statement-2 is True; statement-2 is a correct explanation for Statement-1.

Statement-1 is True, Statement-2 is True; statement-2 is not a correct explanation for Statement-1.

Statement-1 is True, Statement-2 is False.

Statement-1 is False, Statement-2 is True.

Correct Answer:

Statement-1 is False, Statement-2 is True.

Explanation:

We have,

$-1 \leq \sin x \leq 0$  for all  $x \in[\pi, 2 \pi]$

$\Rightarrow -4 \leq 4 \sin x \leq 0$  for all  $x \in[\pi, 2 \pi]$

$\Rightarrow -1 \leq 4 \sin x+3 \leq 3$  for all  $x \in[\pi, 2 \pi]$

$\Rightarrow f(x)=[4 \sin x+3]$  assumes values -1, 0, 1, 2 and 3 when $x \in[\pi, 2 \pi] $

⇒ Range  f = {-1, 0, 1, 2, 3}

So, statement- 2 is true.

Clearly, there are eight points of discontinuity of $f(x)$ in $[\pi, 2 \pi]$. So statement- 1 is not true.