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Question: Answered & Verified by Expert
Let $f: R \rightarrow R$ be such that $f(0)=0$ and $\left|f^{\prime}(x)\right| \leq 5$ for all $x$. Then $f(1)$ is in
MathematicsFunctionsWBJEEWBJEE 2021
Options:
  • A $(5,6)$
  • B $[-5,5]$
  • C $(-\infty,-5) \cup(5, \infty)$
  • D $[-4,4]$
Solution:
1372 Upvotes Verified Answer
The correct answer is: $[-5,5]$
$\left|f^{\prime}(x)\right| \leq 5$
$\int_{0}^{1}-5 d x \leq \int_{0}^{1} f^{\prime}(x) d x \leq \int_{0}^{1} 5 d x$
$\Rightarrow-5 \leq f(1)-0 \leq 5$
$\Rightarrow-5 \leq f(1) \leq 5$
$\Rightarrow f(1) \in[-5,5]$

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