已知平面上有n个点,两点确定一条直线.取第一个点A有n种取法,取第二个点B有(n-1)种取法,所以一共可连成n(n-1)条直线,但AB与BA是同一条直线,故应除以2;即Sn(可连成直线的条数)=n
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![已知平面上有n个点,两点确定一条直线.取第一个点A有n种取法,取第二个点B有(n-1)种取法,所以一共可连成n(n-1)条直线,但AB与BA是同一条直线,故应除以2;即Sn(可连成直线的条数)=n](/uploads/image/z/11804935-31-5.jpg?t=%E5%B7%B2%E7%9F%A5%E5%B9%B3%E9%9D%A2%E4%B8%8A%E6%9C%89n%E4%B8%AA%E7%82%B9%2C%E4%B8%A4%E7%82%B9%E7%A1%AE%E5%AE%9A%E4%B8%80%E6%9D%A1%E7%9B%B4%E7%BA%BF.%E5%8F%96%E7%AC%AC%E4%B8%80%E4%B8%AA%E7%82%B9A%E6%9C%89n%E7%A7%8D%E5%8F%96%E6%B3%95%2C%E5%8F%96%E7%AC%AC%E4%BA%8C%E4%B8%AA%E7%82%B9B%E6%9C%89%EF%BC%88n%EF%BC%8D1%EF%BC%89%E7%A7%8D%E5%8F%96%E6%B3%95%2C%E6%89%80%E4%BB%A5%E4%B8%80%E5%85%B1%E5%8F%AF%E8%BF%9E%E6%88%90n%EF%BC%88n%EF%BC%8D1%EF%BC%89%E6%9D%A1%E7%9B%B4%E7%BA%BF%2C%E4%BD%86AB%E4%B8%8EBA%E6%98%AF%E5%90%8C%E4%B8%80%E6%9D%A1%E7%9B%B4%E7%BA%BF%2C%E6%95%85%E5%BA%94%E9%99%A4%E4%BB%A52%EF%BC%9B%E5%8D%B3Sn%EF%BC%88%E5%8F%AF%E8%BF%9E%E6%88%90%E7%9B%B4%E7%BA%BF%E7%9A%84%E6%9D%A1%E6%95%B0%EF%BC%89%EF%BC%9Dn)
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