[tex] \int\limits x*e^-^x\, dx [/tex]=
[tex](e^-^x)'=e^-^x(-x)' = -e^-^x[/tex]
[tex] \int\limits (-e^-^x)' *x \, dx =
-e^-^x*x- \int\limits -e^-^x * (x)'\, dx=
[/tex]
[tex]=-e^-^x*x- \int\limits -e^-^x \, dx =-e^-^x*x+ \int\limits e^-^x{x} \, dx=
[/tex]
[tex]-e^-^x*x-e^-^x+C [/tex]