7.1 Integration By Parts/11

$\int {\text{arctan(4t)}}dt$

$u={\text{arctan(4t)}}\qquad dv=dt$

$du={\frac {4}{1+(4t)^{2}}}dt\qquad v=t$

${\begin{aligned}\int {\text{arctan(4t)}}dt={\text{t.arctan(4t)}}-4\int {\frac {t}{1+16t^{2}}}dt={\text{tarctan(4t)}}-{\frac {4}{32}}\int {\frac {1}{u}}\\[1ex]&={\text{tarctan(4t)}}-{\frac {1}{8}}\ln(u)={\text{tarctan(4t)}}-{\frac {1}{8}}\ln(1+16t^{2})+C\\[1ex]&\qquad u=1+16t^{2}\\[1ex]&\qquad du=32tdt\\[1ex]&\qquad {\frac {1}{32}}du=tdt\end{aligned}}$