Let $\mathrm{f}(x)=\int \frac{x^2-3 x+2}{x^4+1} \mathrm{~d} x$, then function decreases in the interval

Let $\mathrm{f}(x)=\int \frac{x^2-3 x+2}{x^4+1} \mathrm{~d} x$, then function decreases in the interval
  1. $(-\infty,-2)$
  2. $(-2,-1)$
  3. $(1,2)$
  4. $(2, \infty)$

Solution

$\begin{aligned} & \mathrm{f}(x)=\int \frac{x^2-3 x+2}{x^4+1} \mathrm{~d} x \\ & \Rightarrow \mathrm{f}^{\prime}(x)=\frac{x^2-3 x+2}{x^4+1} \end{aligned}$ For $\mathrm{f}(x)$ to be decreasing, $\begin{aligned} & \mathrm{f}^{\prime}(x) < 0 \\ & \Rightarrow \frac{x^2-3 x+2}{x^4+1} < 0 \\ & \Rightarrow \frac{(x-1)(x-2)}{x^4+1} < 0 \\ & \Rightarrow(x-1)(x-2) < 0 \\ & \Rightarrow x \in(1,2) \end{aligned}$

Asked in: MHT CET 2023 (14 May Shift 1)

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