Medium MCQ +4 / -1 PYQ · JEE Mains 2020

Let a function ƒ : [0, 5] $\to$ R be continuous, ƒ(1) = 3 and F be defined as :

$F(x) = \int\limits_1^x {{t^2}g(t)dt}$ , where $g(t) = \int\limits_1^t {f(u)du}$

Then for the function F, the point x = 1 is :

  1. A a point of inflection.
  2. B a point of local maxima.
  3. C a point of local minima. Correct answer
  4. D not a critical point.

Solution

$F(x) = \int\limits_1^x {{t^2}g(t)dt}$ <br><br>$\Rightarrow$ F'(x) = x<sup>2</sup>g(x) = x<sup>2</sup>$\int\limits_1^t {f(u)du}$ <br><br>$\therefore$ F'(1) = (1)(0) = 0 <br><br>Now, F''(x) = 2xg(x) + x<sup>2</sup>g'(x) <br><br>F''(1) = 2g(1) + g'(1) = 0 + g'(1) = 3 <br><br>[ As g'(t) = f(t); g'(1) = f'(1) = 3 ] <br><br>So, at x = 1, F'(1) = 0 and F"(1) = 3 &gt; 0 <br><br>$\therefore$ For the function f(x), x = 1 is a point of local minima.

About this question

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

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