已知数列{an}满足a1=1,An+1=an/1+2an(n属于N*) 问若若a1a2+a2a3+……+anan+1>1
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已知数列{an}满足a1=1,An+1=an/1+2an(n属于N*) 问若若a1a2+a2a3+……+anan+1>16/33,求n取值范围
已知数列{an}满足A1=1,An+1=An/1+Aan(n属于N*)
问若若A1A2+A2A3+……+AnA(n+1)>16/33,求n取值范围
已知数列{an}满足A1=1,An+1=An/1+Aan(n属于N*)
问若若A1A2+A2A3+……+AnA(n+1)>16/33,求n取值范围
![已知数列{an}满足a1=1,An+1=an/1+2an(n属于N*) 问若若a1a2+a2a3+……+anan+1>1](/uploads/image/z/4059996-60-6.jpg?t=%E5%B7%B2%E7%9F%A5%E6%95%B0%E5%88%97%7Ban%7D%E6%BB%A1%E8%B6%B3a1%3D1%2CAn%2B1%3Dan%2F1%2B2an%28n%E5%B1%9E%E4%BA%8EN%2A%29+%E9%97%AE%E8%8B%A5%E8%8B%A5a1a2%2Ba2a3%2B%E2%80%A6%E2%80%A6%2Banan%2B1%EF%BC%9E1)
An+1=an/1+2an两边去倒数
1/an+1-1/an=2
1/an=1+(n+1)*2=2n+3
an=1/[2n+3]
a1a2+a2a3+……+anan+1=1/2[1/a1-1/a2+1/a2-a/a3+……-1/(2n+3)]=1/2-1/2(2n+3)>16/33
n>15
1/an+1-1/an=2
1/an=1+(n+1)*2=2n+3
an=1/[2n+3]
a1a2+a2a3+……+anan+1=1/2[1/a1-1/a2+1/a2-a/a3+……-1/(2n+3)]=1/2-1/2(2n+3)>16/33
n>15
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