\(A = \int_{1}^{e} xlnxdx.\) Đặt \(\left\{\begin{matrix} u = lnx\\ v = xdx \end{matrix}\right. \Rightarrow \left\{\begin{matrix} du = \frac{dx}{x}\\ v = \frac{x^2}{2} \end{matrix}\right. \Rightarrow A = \frac{x^2 lnx}{2}\bigg |_{1}^{e} - \frac{1}{2}\int_{1}^{e}xdx\)
\(A = \frac{e^2 + 1}{4}\)
\(B = \int_{1}^{e} \frac{lnx}{x}dx\). Đặt \(t = lnx \Rightarrow dt = \frac{dx}{x},\ x = 1 \Rightarrow t = 0,\ x = e \Rightarrow t = 1\)