【高手快来!】数列{a n } 的通项a n =n²(cos²nπ/3-sin²nπ/3),其前n项和为Sn.数列{a n } 的通项a n =n²(cos²nπ/3-sin²nπ/3),其前n项和为Sn.(1)求Sn(2)Bn=(S3n)/(n4^n),求数列{Bn}的
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![【高手快来!】数列{a n } 的通项a n =n²(cos²nπ/3-sin²nπ/3),其前n项和为Sn.数列{a n } 的通项a n =n²(cos²nπ/3-sin²nπ/3),其前n项和为Sn.(1)求Sn(2)Bn=(S3n)/(n4^n),求数列{Bn}的](/uploads/image/z/5086434-66-4.jpg?t=%E3%80%90%E9%AB%98%E6%89%8B%E5%BF%AB%E6%9D%A5%21%E3%80%91%E6%95%B0%E5%88%97%7Ba+n+%7D+%E7%9A%84%E9%80%9A%E9%A1%B9a+n+%3Dn%26%23178%3B%28cos%26%23178%3Bn%CF%80%2F3-sin%26%23178%3Bn%CF%80%2F3%29%2C%E5%85%B6%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn.%E6%95%B0%E5%88%97%7Ba+n+%7D+%E7%9A%84%E9%80%9A%E9%A1%B9a+n+%3Dn%26%23178%3B%28cos%26%23178%3Bn%CF%80%2F3-sin%26%23178%3Bn%CF%80%2F3%29%2C%E5%85%B6%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn.%EF%BC%881%EF%BC%89%E6%B1%82Sn%EF%BC%882%EF%BC%89Bn%3D%EF%BC%88S3n%EF%BC%89%2F%EF%BC%88n4%5En%EF%BC%89%2C%E6%B1%82%E6%95%B0%E5%88%97%7BBn%7D%E7%9A%84)
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