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