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

$$\mathop {\lim }\limits_{x \to 0} {{\int\limits_0^{{x^2}} {\left( {\sin \sqrt t } \right)dt} } \over {{x^3}}}$$ is equal to :

  1. A ${1 \over {15}}$
  2. B 0
  3. C ${2 \over 3}$ Correct answer
  4. D ${3 \over 2}$

Solution

$$\mathop {\lim }\limits_{x \to {0^ + }} {{\int\limits_0^{{x^2}} {\sin (\sqrt t )dt} } \over {{x^3}}}$$<br><br>This is in ${0 \over 0}$ form, so use L' Hospital rule<br><br>$$ = \mathop {\lim }\limits_{x \to {0^ + }} {{{d \over {dx}}\left( {\int\limits_0^{{x^2}} {\sin (\sqrt t )dt} } \right)} \over {{d \over {dx}}\left( {{x^3}} \right)}}$$<br><br>$= \mathop {\lim }\limits_{x \to {0^ + }} {{\sin x.2x - 0} \over {3{x^2}}}$<br><br>(applying Leibnitz rule)<br><br>$= {2 \over 3}\mathop {\lim }\limits_{x \to {0^ + }} {{\sin x} \over x}$<br><br>$= {2 \over 3}$

About this question

Subject: Mathematics · Chapter: Definite Integration · Topic: Properties of Definite Integrals

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