题目

数列{an}中，a1，a2－a1，a3－a2，…，an－an－1…是首项为1、公比为的等比数列，则an等于            。 答案：（1－） 解析:an=a1+（a2－a1）+（a3－a2）+…+（an－an－1）=（1－）。Scientists often see the first ten years of a child’s life as the “window of opportunity.”   1.  And studies show that the following activities can benefit their brain greatly.  2.  Free playtime has always been an important part of “being a kid”, but it is also important to a child’s development. “Free play” not only helps kids develop different skills, it also helps them develop into happy healthy adults in the future. Read with kids Reading has long been known to improve children’s intelligence.   3.  For parents who don’t have much time, just surrounding your kids with books goes a long way too. Put kids to bed early  4.  Preschool children should get at least eleven hours of sleep and kids up to age 12 should try to get at least ten hours of sleep. Learn a second language Early studies in this field have shown that bilingual (双语的) kids can perform better under pressure. Young children can learn new languages with nearly perfect fluency (流利) and pronunciation. Praise good effort not intelligence. Your kids may be smart but you should mainly praise the effort they put into tasks. Kids, who are praised on intelligence, often feel it is a fixed quality, and mistakes or failures badly hurt their self-confidence. Kids who are praised on effort often focus more on learning.   5.     A．Play some helpful games. B．Give them enough playtime. C．And they are not afraid to fail and try again. D．Kids still need time away from the TV to do homework. E. Kids who read often develop earlier writing and number skills as well. F. Everything at this time is very important to the development of a person’s brain. G. Studies show that kids with regular bedtimes are better at languages, math and reading.