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Example · Example 4

Q.Evaluate ∫xsin⁡x dx\displaystyle\int x\sin x\,dx.

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By ILATE, xx (algebraic) outranks sin⁡x\sin x (trigonometric), so u=xu=x (du=dxdu=dx) and

dv=sin⁡x dxdv=\sin x\,dx (v=−cos⁡xv=-\cos x). By parts:

∫xsin⁡x dx=x(−cos⁡x)−∫(−cos⁡x) dx=−xcos⁡x+∫cos⁡x dx=−xcos⁡x+sin⁡x+C.\int x\sin x\,dx = x(-\cos x)-\int(-\cos x)\,dx = -x\cos x+\int\cos x\,dx = -x\cos x+\sin x+C. …

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