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等差数列{an}中,a1+a2+…+a50=200,a51+a52+…+a100...
等差数列{an}中,a1+a2+…+a50=200,a51+a52+…+a100=2700,则a1等于( )
A.-1221
B.-21.5
C.-20.5
D.-20
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