$\int_{1}^{2} \frac{\mathrm{d} x}{x(1+\log x)^{2}}=$

$\int_{1}^{2} \frac{\mathrm{d} x}{x(1+\log x)^{2}}=$
  1. $\cdot \log 2$
  2. $1+\log 2$
  3. $\log (1+\log2)$
  4. $\frac{1}{(1+\log 2)}$

Solution

$I=\int_{1}^{2} \frac{d x}{x(1+\log x)}$ Put $\quad 1+\log x=t \Rightarrow \frac{1}{x} d x=d t$ When $x=1, t=1$ and when $x=2, t=1+\log 2$ $\begin{aligned} I &=\int_{1}^{1+\log 2} \frac{d t}{t}=[\log t]_{1}^{1+\log 2}=\log (1+\log 2)-\log 1 \\ &=\log (1+\log 2) \end{aligned}$

Asked in: MHT CET 2020 (20 Oct Shift 1)

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