y = x e − 0.4 x x = 0 , x = 1 {\displaystyle y=xe^{-0.4x}~~~x=0,x=1}
∫ 0 5 x e − 0.4 x d x ⏟ u = x {\displaystyle \underbrace {\int _{0}^{5}xe^{-0.4x}dx} u~~~=~~~~x}
