7.1 Integration By Parts/19

${\begin{aligned}\int _{0}^{\pi }(tsin3t)dt\\[2ex]&=\int _{0}^{\pi }{\frac {1}{2}}t^{2}{\frac {1}{2}}sin3t^{2}\\[2ex]&=\int _{0}^{\pi }{\frac {1}{2}}\pi ^{2}{\frac {1}{2}}sin3\pi ^{2}\\[2ex]&={\frac {\pi }{3}}\end{aligned}}$