Easy MCQ +4 / -1 PYQ · JEE Mains 2021

Let f be any function defined on R and let it satisfy the condition : $|f(x) - f(y)|\, \le \,|{(x - y)^2}|,\forall (x,y) \in R$

If f(0) = 1, then :

  1. A f(x) can take any value in R
  2. B $f(x) < 0,\forall x \in R$
  3. C $f(x) > 0,\forall x \in R$ Correct answer
  4. D $f(x) = 0,\forall x \in R$

Solution

$|f(x) - f(y)|\, \le \,|{(x - y)^2}|$<br><br>$\Rightarrow \left| {{{f(x) - f(y)} \over {x - y}}} \right|\, \le \,|x - y|$<br><br>$$ \Rightarrow \left| {\mathop {\lim }\limits_{x \to y} {{f(x) - f(y)} \over {x - y}}} \right|\, \le \,|\mathop {\lim }\limits_{x \to y} (x - y)|$$<br><br>$\Rightarrow |f'(x)|\, \le 0$<br><br>$\Rightarrow f'(x) = 0$<br><br>$\Rightarrow f(x)$ is constant function.<br><br>$\because$ $f(0)$ = 1 then f(x) = 1

About this question

Subject: Mathematics · Chapter: Application of Derivatives · Topic: Tangents and Normals

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