i need some clarification about the problem below;

$\displaystyle \int_{-1.2}^{3.9} xd[x] $

the only way i understand to solve the above problem is to apply integration by part

that is

$\displaystyle \int_{-1.2}^{3.9} xd[x] + \int_{-1.2}^{3.9} |x|dx = f(b)g(a) - f(a)g(a) $

do i just substitutea as -1.2andb as 3.9and that's all?

pls help here

and again how do one disband modulus sign from integration function? asking for general purpose

thanks