高等数学

计算 \[ I=\int _{0}^{\pi }\dfrac{x\sin x}{1+\cos ^{2}x}dx \]

每日一句长难句

Your humor must be relevant to the audience and should help to show them that you are one of them or that you understand their situation and are in sympathy with their point of view. [2002 英语一TEXT1]