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Find the value of the integral ∫ In(x)dx(x)dx(x)dx.
Question

Find the value of the integral ∫ In(x)dx(x)dx.

A.

xln(x)x+Cxln(x)-x+C ​​

B.

xln(x)1+Cxln(x)-1+C ​​

C.

xln(x)+1x+C-xln(x)+\frac{1}{x}+C ​​

D.

1xln(x)x+C\frac{1}{x}ln(x)-x+C ​​

Correct option is A

Let:u=ln(x)=>dudx=1xdv=dx=>v=xApply the integration by parts formula:u dv=uvv duSo,ln(x) dx=xln(x)x1x dx=xln(x)1 dx=xln(x)x+C\begin{aligned}&\text{Let:} \\&\quad u = \ln(x) \Rightarrow \frac{du}{dx} = \frac{1}{x} \\&\quad dv = dx \Rightarrow v = x \\\\&\text{Apply the \textbf{integration by parts} formula:} \\&\quad \int u \, dv = uv - \int v \, du \\\\&\text{So,} \\&\int \ln(x) \, dx = x \ln(x) - \int x \cdot \frac{1}{x} \, dx = x \ln(x) - \int 1 \, dx \\&= x \ln(x) - x + C\end{aligned}​​

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