等比数列练习题,1、再等比数列{an}中,公比为q,a1+a2+a3=18,a2+a3+a4=-9,则a1比1-q为_____.2、在1/n与n+1两数之间插入n个正数,使这n+2个数成等比数列,求插入的n个数之积.3、已知1,x1,x2···,x2n,2成等比数列
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![等比数列练习题,1、再等比数列{an}中,公比为q,a1+a2+a3=18,a2+a3+a4=-9,则a1比1-q为_____.2、在1/n与n+1两数之间插入n个正数,使这n+2个数成等比数列,求插入的n个数之积.3、已知1,x1,x2···,x2n,2成等比数列](/uploads/image/z/12664296-0-6.jpg?t=%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97%E7%BB%83%E4%B9%A0%E9%A2%98%2C1%E3%80%81%E5%86%8D%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97%7Ban%7D%E4%B8%AD%2C%E5%85%AC%E6%AF%94%E4%B8%BAq%2Ca1%2Ba2%2Ba3%3D18%2Ca2%2Ba3%2Ba4%3D-9%2C%E5%88%99a1%E6%AF%941-q%E4%B8%BA_____.2%E3%80%81%E5%9C%A81%2Fn%E4%B8%8En%2B1%E4%B8%A4%E6%95%B0%E4%B9%8B%E9%97%B4%E6%8F%92%E5%85%A5n%E4%B8%AA%E6%AD%A3%E6%95%B0%2C%E4%BD%BF%E8%BF%99n%2B2%E4%B8%AA%E6%95%B0%E6%88%90%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97%2C%E6%B1%82%E6%8F%92%E5%85%A5%E7%9A%84n%E4%B8%AA%E6%95%B0%E4%B9%8B%E7%A7%AF.3%E3%80%81%E5%B7%B2%E7%9F%A51%2Cx1%2Cx2%C2%B7%C2%B7%C2%B7%2Cx2n%2C2%E6%88%90%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97)
等比数列练习题,1、再等比数列{an}中,公比为q,a1+a2+a3=18,a2+a3+a4=-9,则a1比1-q为_____.2、在1/n与n+1两数之间插入n个正数,使这n+2个数成等比数列,求插入的n个数之积.3、已知1,x1,x2···,x2n,2成等比数列
等比数列练习题,
1、再等比数列{an}中,公比为q,a1+a2+a3=18,a2+a3+a4=-9,则a1比1-q为_____.
2、在1/n与n+1两数之间插入n个正数,使这n+2个数成等比数列,求插入的n个数之积.
3、已知1,x1,x2···,x2n,2成等比数列,求积x1,x2···x2n.
等比数列练习题,1、再等比数列{an}中,公比为q,a1+a2+a3=18,a2+a3+a4=-9,则a1比1-q为_____.2、在1/n与n+1两数之间插入n个正数,使这n+2个数成等比数列,求插入的n个数之积.3、已知1,x1,x2···,x2n,2成等比数列
1.(a1+a2+a3)/(a2+a3+a4)=a1(1+q+qq)/[a1qq(1+q+qq)=1/q=-2
q=-1/2
a1+a2+a3=a1(1+q+qq)=18
a1=-72
a1/(1-q)=-72/(1+1/2)=-48
2.因为a1=1/n,an=a1*q^(n-1),
所以a(n+2)=a1*q^(n+1)=(1/n)*q^(n+1)=n+1
即q^(n+1)=(n+1)*n
q1*q2*q3*……*qn=q^(1+2+3+……+n)=q^(1+n)*n/2
=[(n+1)*n]^1/2
=根号下〔(n+1)*n〕
3.因为an=a1*q^(n-1),
a1=1,a的2n+2项=2
所以
2=1*q^(2n+1)即q^(2n+1)=2
x1*x2*x3*……x2n
=q^1*q^2*q^3*……*q^2n
=q^(1+2+3+……+2n)
=q^[(1+2n)*2n/2]
=q^[n*(2n+1)]
=[q^(2n+1)]^n
=2^n