∫ arctg 2xdx
[m]du=\frac{2}{1+(2x)^2}dx[/m]
[m]dv=dx[/m]
[m]v=x[/m]
[m]∫ arctg 2x dx=(arctg 2x)*x- ∫ x*\frac{2}{1+(2x)^2}dx[/m]=
[m]=x*arctg 2x- ∫ d(1+x^2)/(1+x^2)=[/m]
[m]=x*arctg 2x- ln|1+x^2|+C=[/m]
[m]=x*arctg 2x- ln(1+x^2)+C[/m]