等差数列问题

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0 | 2010-4-22 21:04:17 | 显示全部楼层 |阅读模式

b1b2b3=(1/2)^a1*(1/2)^a2*(1/2)^a3=(1/2)^(a1+a2+a3)=1/8=(1/2)^3所以a1+a2+a3=3an等差a1+a2+a3=3a2=3a2=1a1=1-d,a3=1+db1+b2+b3=(1/2)^(1-d)+1/2+(1/2)^(1+d)=21/8(1/2)^(1-d)+(1/2)^(1+d)=17/8令a=(1/2)^d则(1/2)^(1-d)=1/2÷a(1/2)^(1+d)=1/2*a所以1/(2a)+a/2=17/84+4a2=17aa=4,a=1/4(1/2)^d=a所以d=±2所以a1=-1,a2=1,a3=3或a1=3a2=1,a3=-1参考资料：http://zhidao.baidu.com/question/141789371.html?push=ql