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

Let f(x) be a differentiable function at x = a with f'(a) = 2 and f(a) = 4.

Then $\mathop {\lim }\limits_{x \to a} {{xf(a) - af(x)} \over {x - a}}$ equals :

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

Solution

$L = \mathop {\lim }\limits_{x \to a} {{xf(a) - af(x)} \over {x - a}}$ [${0 \over 0}$ form] <br><br>Using L' Hospital rule we get<br><br>$L = \mathop {\lim }\limits_{x \to a} {{f(a) - af'(x)} \over 1}$<br><br>$f(a) - af'(a) = 4 - 2a$

About this question

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

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