已知正项等比数列{an}中,a2×a (n-1)+a4 ×a(n-3)=200,则lga1+lga2+...lgan=?
已知正项等比数列{an}中,a2×a (n-1)+a4 ×a(n-3)=200,则lga1+lga2+...lgan=?
数学人气:432 ℃时间:2020-04-15 18:39:00
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正项等比数列{an}中,a2×a (n-1)+a4 ×a(n-3)=200所以,a1×an=a2×a (n-1)=a3×a(n-2)=a4 ×a(n-3)=……200÷2=100n为偶数时,一共有n/2对则,lga1+lga2+...lgan=lg(a1an)+lg[a2a(n-1)]+…… (n/2个)=2+...
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