已知a1=3,a(n+1)=(3n-1)/(3n+2)an(n≥1),求an
人气:103 ℃ 时间:2019-12-17 10:28:28
解答
a2/a1=2/5,
a3/a2=5/8,
a4/a3=8/11,
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.
.
an+1/an=(3n-1)/(3n+2)
左相乘:(a2/a1)(a3/a2)(a4/a3)……(an+1/an)=右相乘:2/5 5/8 8/11……(3n-1)/(3n+2),
an+1/a1=2/(3n+2),
an+1/3=2/(3n+2),
an+1=6/(3n+2),
an=6/(3n-1).
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