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在各项都是正数的等比数列{an}中,a1=3,a1+a2+a3=21,则a4+a...
在各项都是正数的等比数列{an}中,a1=3,a1+a2+a3=21,则a4+a5+a6=( )
A.63
B.168
C.84
D.189
考点分析:
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