已知数列{an}满足a1=5,anan+1=2的n次方,则a7/a3=

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已知数列{an}满足a1=5,anan+1=2的n次方,则a7/a3=

已知数列{an}满足a1=5,anan+1=2的n次方,则a7/a3=
已知数列{an}满足a1=5,anan+1=2的n次方,则a7/a3=

已知数列{an}满足a1=5,anan+1=2的n次方,则a7/a3=
方法一:数不多,一个一个写
a(n+1)=2^n/(an)
a1=5
a2=2/5
a3=4/(2/5)=10
a4=8/(10)=4/5
a5=16/(4/5)=20
a6=32/(20)=8/5
a7=64/(8/5)=40
∴ a7/a3=4
方法二
an*a(n+1)=2^n
∴ a(n-1)*an=2^(n-1)
两式子相除
则 a(n+1)/a(n-1)=2
∴ a7/a5=2,a5/a3=2
∴ a7/a3=4

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