If $\mathrm{f}(\mathrm{x})=\frac{1}{\log \mathrm{x}}, \mathrm{g}(\mathrm{x})=\frac{1}{(\log \mathrm{x})^2}$,…

If $\mathrm{f}(\mathrm{x})=\frac{1}{\log \mathrm{x}}, \mathrm{g}(\mathrm{x})=\frac{1}{(\log \mathrm{x})^2}$, then find \(\int\{f(x)-g(x)\} d x\) (Where C is a constant of integration.)
  1. $(\log x)^2+C$
  2. $x \log x+C$
  3. $\frac{x}{\log x}+C$
  4. $\frac{1}{\log x}+C$

Solution

$\begin{aligned} & \int\{f(x)-g(x)\} d x=\int f(x) d x-\int g(x) d x \\ & =\int \frac{1}{\log x} d x-\int \frac{1}{(\log x)^2} d x \\ & =\int \frac{1}{\log x} \times 1 d x-\int \frac{1}{(\log x)^2} d x \\ & =\frac{1}{\log x} \cdot x-\int \frac{-1}{(\log x)^2} \times \frac{1}{x} \times x d x-\int \frac{1}{(\log x)^2} d x \\ & =\frac{x}{\log x}+\int \frac{1}{(\log x)^2} d x-\int \frac{d x}{(\log x)^2} \\ & =\frac{x}{\log x}\end{aligned}$

Asked in: MHT CET 2022 (06 Aug Shift 1)

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