www.1862.net > 已知等比数列{An}中A(n+1)>An,且A3+A7=3,A2A8...

已知等比数列{An}中A(n+1)>An,且A3+A7=3,A2A8...

(1)q^3=a7/a4=8/2=4 q=4^(1/3)=2^(2/3) a1=a4/q^3=2/4=1/2 an=a1*q^(n-1)=1/2*(2^(2/3))^(n-1)=2^(-1+2n/3-2/3)=2^(2n/3-5/3) (2) a2+a5=a2(1+q^3)=18 a3+a6=a3(1+q^3)=9 下式/上式得:q=a3/a2=1/2 a2+a5=a1*1/2+a1*(1/2)^4=18 a1=32 an=a1*q...

a2a4a6=8,可推出:a1q³=2 a3a5a7=27,可推出:a1q^4=3 a1a7十2a4a5十a2a8 =(a1q³)²+2(a1q³xa1q^4)+(a1q^4)² =2²+2x2x3+3² =4+12+9 =25 求采纳!!

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