letf(t) dt = dF(t)g(x) = ∫ (1->x) xf(t) dt = x[F(x)- F(1) ]g'(x) = [F(x)- F(1) ] - F'(x) =∫ (1->x) f(t) dt - f(x)ied/dx [∫ (1->x) xf(t) dt] = ∫ (1->x) f(t) dt - f(x)
