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Question: Answered & Verified by Expert
If $f(x)$ is a function such that $f^{\prime}(x)=(x-1)^{2}(4-x),$ then
MathematicsApplication of DerivativesWBJEEWBJEE 2016
Options:
  • A $f(0)=0$
  • B $f(x)$ is increasing in (0,3)
  • C $x=4$ is a critical point of $f(x)$
  • D $f(x)$ is decreasing in (3,5)
Solution:
1281 Upvotes Verified Answer
The correct answers are: $f(x)$ is increasing in (0,3), $x=4$ is a critical point of $f(x)$
Given
$$
f^{\prime}(x)=(x-1)^{2}(4-x)
$$
The sign scheme of $f^{\prime}(x)$


Clearly. $f(x)$ is increasing, for $x \in(-\infty, 4)$ and decreasing, for $n \in(4, \infty)$
Since, $f^{\prime}(x)=0$ at $x=4$
$\mathrm{SO}, \mathrm{x}=4$ is a critical point.

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