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A.an+1=anq(q为常数) B.an+12=anan+2≠0
C.an=a1qn-1(q为常数) D.an+1=
A.an+1=anq(q为常数)
B.an+12=an·an+2≠0
C.an=a1qn-1(q为常数)
D.
D.an+1=
数列{an}成等比数列的充分必要条件是( )