Medium MCQ +4 / -1 PYQ · JEE Mains 2021

Let $f:\left( { - {\pi \over 4},{\pi \over 4}} \right) \to R$ be defined as $$f(x) = \left\{ {\matrix{ {{{(1 + |\sin x|)}^{{{3a} \over {|\sin x|}}}}} & , & { - {\pi \over 4} < x < 0} \cr b & , & {x = 0} \cr {{e^{\cot 4x/\cot 2x}}} & , & {0 < x < {\pi \over 4}} \cr } } \right.$$

If f is continuous at x = 0, then the value of 6a + b2 is equal to :

  1. A 1 $-$ e
  2. B e $-$ 1
  3. C 1 + e Correct answer
  4. D e

Solution

$\mathop {\lim }\limits_{x \to 0} f(x) = b$<br><br>$$\mathop {\lim }\limits_{x \to {0^ + }} x{e^{{{\cot 4x} \over {\cot 2x}}}} = {e^{{1 \over 2}}} = b$$<br><br>$$\mathop {\lim }\limits_{x \to {0^ - }} {(1 + |\sin x|)^{{{3a} \over {|\sin x|}}}} = {e^{3a}} = {e^{{1 \over 2}}}$$<br><br>$a = {1 \over 6} \Rightarrow 6a = 1$<br><br>$\therefore$ $(6a + {b^2}) = (1 + e)$

About this question

Subject: Mathematics · Chapter: Limits, Continuity and Differentiability · Topic: Limits and Standard Results

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