Mr. Smith worked in a post office and three years ago, when he was sixty, he retired. So he has a lot of free time now. He likes neither reading nor watching TV. He feels bored and he goes to visit
任务性阅读 Today is Kate’s birthday and she’s fifteen. Now she is with her family. Let’s meet her family. Her father’s name is Smith. He works in a hospital. People think①他
81-year-old man helped poor studentsOn December 2, 2009, in No.1 High School, Yaling Town, Yichuan County, Luoyang, an old man with a stick is taking 300 notebooks and 120 ball pens out of a bag. He i
中，若前n项积为
，则有
，在等差数列
中，若前n项和为
，用类比的方法得到的结论是 。
