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JEE Main 20203 SeptemberEvening Shift
Exam
JEE Main
Year
2020
Date
3 September
Shift
Evening Shift
Subject
Mathematics
Chapter
Limits

JEE Main 2020 · 3 September · Evening Shift · Mathematics · Limits

_ x → a (a + 2x)(1)/(3) -(3x)(1)/(3) (3a + x\ right)(1)/(3) -(4x)...

\lim_{x \to a}\dfrac{\left(a + 2x\right)\dfrac{1}{3} -\left(3x\right)\dfrac{1}{3}}{ \left(3a + x\$right)13−(4x)\dright)\dfrac{1}{3} -\left(4x\right)\ddfrac{1}{3}}\left(a \ne 0\right)$& is equal to:

Options

  1. A\left(\dfrac{2}{9}\right)(23)13\left(\dfrac{2}{3}\right)\dfrac{1}{3}
  2. B(23)43\left(\dfrac{2}{3}\right)\dfrac{4}{3}
  3. C(29)43\left(\dfrac{2}{9}\right)\dfrac{4}{3}
  4. D\left(\dfrac{2}{3}\right)(29)13\left(\dfrac{2}{9}\right)\dfrac{1}{3}

Correct answer

D. \left(\dfrac{2}{3}\right)(29)13\left(\dfrac{2}{9}\right)\dfrac{1}{3}

Step-by-step solution

At x=ax = a, limit is of 00\dfrac{0}{0} form.

So, applying L'Hospital rule, we get

lim⁡x→a(a+2x)13−(3x)13(3a+x)13−(4x)13=lim⁡x→a13(a+2x)−23.2−13.(3x)−23.313(3a+x)−23.−13.(4x)−23.4\lim_{x \to a}\dfrac{{\left(a + 2x\right)}^{\dfrac{1}{3}} - \left(3x\right)\dfrac{1}{3}}{\left(3a + x\right)\dfrac{1}{3} - \left(4x\right)\dfrac{1}{3}} = \lim_{x \to a}\dfrac{\dfrac{1}{3}{\left(a + 2x\right)}^{- \dfrac{2}{3}} . 2 - \dfrac{1}{3} . {\left(3x\right)}^{- \dfrac{2}{3}} . 3}{\dfrac{1}{3}{\left(3a + x\right)}^{- \dfrac{2}{3}} . - \dfrac{1}{3} . {\left(4x\right)}^{- \dfrac{2}{3}} . 4}

=13(3a)−23.(2−3)13(4a)−23.(1−4)=3−234−23.13= \dfrac{\dfrac{1}{3}{\left(3a\right)}^{- \dfrac{2}{3}} . \left(2 - 3\right)}{\dfrac{1}{3}{\left(4a\right)}^{- \dfrac{2}{3}} . \left(1 - 4\right)} = \dfrac{{3}^{- \dfrac{2}{3}}}{{4}^{- \dfrac{2}{3}}} . \dfrac{1}{3}

=243913.13=(23)(29)13= \dfrac{2\dfrac{4}{3}}{9\dfrac{1}{3}} . \dfrac{1}{3} = \left(\dfrac{2}{3}\right)\left(\dfrac{2}{9}\right)\dfrac{1}{3}

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