f(x)= xsin(x) >>>>>>>>>>>>>>>>>> integral[ udv/dx ] dx= uv - integral[v* du/dx] dx
let x=u and sin(x)=dv/dx >>>>>>>>>>>>>>>>>> du/dx=1 , v= -cos(x)
Plugging in gives formula: integral[ xsin(x)] dx = (x)(-cos(x)) - integral[ -cos(x) ]dx
solving gives ............... = sin(x) - xcos(x) + C