已知数列 an 的首相为a1=2,且an+1=1/2(a1+a2+……+an)(n∈N+),记Sn为数列{an}的前n项和,则Sn=?
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![已知数列 an 的首相为a1=2,且an+1=1/2(a1+a2+……+an)(n∈N+),记Sn为数列{an}的前n项和,则Sn=?](/uploads/image/z/3930475-67-5.jpg?t=%E5%B7%B2%E7%9F%A5%E6%95%B0%E5%88%97+an+%E7%9A%84%E9%A6%96%E7%9B%B8%E4%B8%BAa1%3D2%2C%E4%B8%94an%2B1%3D1%2F2%28a1%2Ba2%2B%E2%80%A6%E2%80%A6%2Ban%29%28n%E2%88%88N%2B%29%2C%E8%AE%B0Sn%E4%B8%BA%E6%95%B0%E5%88%97%EF%BD%9Ban%EF%BD%9D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%2C%E5%88%99Sn%3D%3F)
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已知数列 an 的首相为a1=2,且an+1=1/2(a1+a2+……+an)(n∈N+),记Sn为数列{an}的前n项和,则Sn=?
已知数列 an 的首相为a1=2,且an+1=1/2(a1+a2+……+an)(n∈N+),记Sn为数列{an}的前n项和,则Sn=?
已知数列 an 的首相为a1=2,且an+1=1/2(a1+a2+……+an)(n∈N+),记Sn为数列{an}的前n项和,则Sn=?
an=1/2*s(n-1),2an=s(n-1),2(sn-s(n-1))=s(n-1),2sn=3s(n-1),
sn=3/2(a(n-1)),sn=(3/2)^(n-1)s1,sn=(3/2)^(n-1)a1
sn=3^(n-1)/2^(n-2)