题目

An English Lecture Do you have any problems when you are learning English? Come to the lecture（演讲）on Friday afternoon! Simon Greenall will give the lecture in the Science Hall. The address is No.125, Beijing Road. Get more information by calling 83156322.Beijing Opera Do you like listening to Beijing Opera? Come and join us on Saturday morning. Remember: No slippers（拖鞋）! The opera will begin at 9:30 in the Great Theater. Please go in and be seated（就座）ten minutes earlier. The tickets are free.A Concert Do you like classical music? Come to the concert（音乐会）on Sun(2005浙江台州)我国的代数学家秦九韶在《数书九章》中记述了“三斜求积术”，即已知三角形的三边长，求它的面积，用现代式子表示为：　①(其中a、b、c为三角形的三边长，s为面积)．而另一个文明古国古希腊也有求三角形面积的海伦公式：　②． (1)若已知三角形的三边长分别为5、7、8，试分别运用公式①和公式②，计算该三角形的面积s； (2)你能否由公式①推导出公式②？请试试．