问题
填空题
若数列{an}满足a1，a2-a1，a3-a2，…，an-an-1，…，是首项为1，公比为2的等比数列，那么an等于______．
答案
由题意可知，an=a1+（a2-a1）+（a3-a2）+…+（an-an-1）
=
=2n-1．1×(1-2n) 1-2
故答案为2n-1
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若数列{an}满足a1，a2-a1，a3-a2，…，an-an-1，…，是首项为1，公比为2的等比数列，那么an等于______．
由题意可知，an=a1+（a2-a1）+（a3-a2）+…+（an-an-1）
=
=2n-1．1×(1-2n) 1-2
故答案为2n-1
Once, a circle lost a piece of its own. The circle wanted to be whole, so it went around, looking for its piece. But because it was not complete, it could only roll (滚) very slowly. It enjoyed the flowers and the sunshine the way. It talked with worms. It found lots of different pieces, but of them fit. So it left them all by the side of the road and kept on for the lost piece. Then one day the circle found a piece that fit . The circle put the piece into . It could be whole with nothing lost. It was so happy and began to roll. As it was a perfect circle, it could roll very fast, too fast to see flowers or talk to worms. It realized how different the world was when it rolled so quickly. It felt so sad it stopped, left its found piece by the side of the road and rolled very slowly. Sometimes we are perfect when we lose something. A man has everything is poor in some ways. He will never have hopes, dreams or something . He will never know someone loves him or someone is giving him something he has always wanted or never had. We couldn’t be perfect. But we must be brave enough to love, strong enough to forgive, kind enough to share with others and clever enough to know there is enough love around us and then we can always have a wonderful time in our life.
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