\(Let\ I=\)\(∫x sin\ x dx\)
Taking x as first function and \(sin \ x\) as second function and integrating by parts, we obtain
\(I =\) \(x∫sin\ x dx-∫[{(\frac {d}{dx} x)∫sin\ x dx}]dx\)
\(I =\)\(x(-cosx)-∫1.(-cosx)dx\)
\(I =-xcos\ x+sin\ x+C\)
The number of formulas used to decompose the given improper rational functions is given below. By using the given expressions, we can quickly write the integrand as a sum of proper rational functions.
For examples,