$\int_{2}^{3} \frac{d x}{x^{2}+x}=$

$\int_{2}^{3} \frac{d x}{x^{2}+x}=$
  1. $\log \left(\frac{3}{4}\right)$
  2. $\log \left(\frac{3}{2}\right)$
  3. $\log \left(\frac{9}{8}\right)$
  4. $\log \left(\frac{8}{9}\right)$

Solution

$\begin{aligned} \mathrm{I} &=\int_{2}^{3} \frac{\mathrm{dx}}{\mathrm{x}^{2}+\mathrm{x}}=\int_{2}^{3} \frac{\mathrm{dx}}{\mathrm{x}(\mathrm{x}+1)} \\ \therefore \mathrm{I} &=\int_{2}^{3}\left[\frac{1}{\mathrm{x}}-\frac{1}{\mathrm{x}+1}\right] \mathrm{dx} \\ &=[\log \mathrm{x}-\log (\mathrm{x}+1)]_{2}^{3}=\left[\log \left(\frac{\mathrm{x}}{\mathrm{x}+1}\right)\right]_{2}^{3} \\ &=\log \left(\frac{3}{4}\right)-\log \left(\frac{2}{3}\right)=\log \left(\frac{3}{4} \times \frac{3}{2}\right)=\log \left(\frac{9}{8}\right) \end{aligned}$

Asked in: MHT CET 2020 (12 Oct Shift 2)

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