Medium MCQ +4 / -1 PYQ · JEE Mains 2022

If m and n respectively are the number of local maximum and local minimum points of the function $f(x) = \int\limits_0^{{x^2}} {{{{t^2} - 5t + 4} \over {2 + {e^t}}}dt}$, then the ordered pair (m, n) is equal to

  1. A (3, 2)
  2. B (2, 3) Correct answer
  3. C (2, 2)
  4. D (3, 4)

Solution

<p>$f(x) = \int_0^{{x^2}} {{{{t^2} - 5t + 4} \over {2 + {e^t}}}dt}$</p> <p>$f'(x) = 2x\left( {{{{x^4} - 5{x^2} + 4} \over {2 + {e^{{x^2}}}}}} \right) = 0$</p> <p>$x = 0$, or $({x^2} - 4)({x^2} - 1) = 0$</p> <p>$x = 0,$ $x = \pm 2,\, \pm 1$</p> <p>Now, $$f'(x) = {{2x(x + 1)(x - 1)(x + 2)(x - 2)} \over {\left( {{e^{{x^2}}} + 2} \right)}}$$</p> <p>f'(x) changes sign from positive to negative at x = $-$1, 1 So, number of local maximum points = 2</p> <p>f'(x) changes sign from negative to positive at x = $-$2, 0, 2 So, number of local minimum points = 3</p> <p>$\therefore$ m = 2, n = 3</p>

About this question

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

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