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Exercise: Integration by Parts · Q20

Q.Evaluate ∫ln⁡x dx\displaystyle\int \ln x\,dx.

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Write ln⁡x=1⋅ln⁡x\ln x=1\cdot\ln x, so u=ln⁡xu=\ln x (du=dx/xdu=dx/x), dv=dxdv=dx (v=xv=x):

∫ln⁡x dx=xln⁡x−∫x⋅1x dx=xln⁡x−∫dx=xln⁡x−x+C.\int\ln x\,dx = x\ln x-\int x\cdot\frac1x\,dx = x\ln x-\int dx = x\ln x-x+C. …

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