已知数列{an}满足a1=2,a(n+1)=2an/(an+2),证明:数列{1/an}为等差数列

问题描述:

已知数列{an}满足a1=2,a(n+1)=2an/(an+2),证明:数列{1/an}为等差数列

1/a(n+1)-1/an=(an+2)/2an-1/an=an/2an=1/2

a(n+1)=2an/(an+2),a1=2,说明an>0∵a(n+1)=2an/(an+2),∴1/a(n+1)=(an+2)/2an=1/an+1/2∴1/a(n+1)-1/an=1/2,a1=2所以{1/an}为等差数列