\(Let\ I=∫xsin\ 3xdx\)
Taking x as first function and \(sin\ 3x\) as second function and integrating by parts, we obtain
\(I= x∫sin\ 3x dx-∫{(\frac {d}{dx}x)∫sin\ 3x dx}\)
\(I = x(\frac {-cos\ 3x}{3})-∫1.(\frac {-cos\ 3x}{3})dx\)
\(I = \frac {-xcos\ 3x}{3}+\frac 13∫cos\ 3x dx\)
\(I = \frac {-xcos \ 3x}{3}+\frac 19sin\ 3x+C\)
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,