在等比数列an中a5=4a7=6-搜答案-大师作文网

(a7-a5)/(a6+a5)=(q^2-1)/(q+1)=1所以,q=2或-1(舍)a5+a6=a1(q^4+q^5)=48将q=2代入上式得,a1=1所以,s10=a1(1-q^10)/(1-q)

1.a6*a7*a8=a5*q*a6*q*a7*q=a5*a6*a7*q³=3q³=24所以公比q=2a7*a8*a9=a6*q*a7*q*a8*q=24*2³=1922

an=a1q^(n-1)a1+a3=30a1(1+q^2)=30(1)a5+a7=120a1q^4(1+q^2)=120(2)(2)/(1)q^4=40a9+a11=a1q^8(1+q^2)=30q^

/>a7+a6=(a7-a5)+(a6+a5)=48+48=96q=(a7+a6)/(a6+a5)=96/48=2a6=2a5a6+a5=3a5=48a5=16a1=a5/q^4=1S10=(2^10

a5/a1=q^4a7/a3=q^4所以(a5+a7)/(a1+a3)=5/10=q^4=1/2a9/a5=q^4a11/a7=q^4所以（a9+a11)/(a5a+7)=q^4=1/2所以a9+a1

a4=a1q^3a5=a1q^4a6=a1q^5a7=a1q^6a1q^3*a1q^6=32即a1^2q^9=32(1)a1q^4+a1q^5=12a1q^4(1+q)=12平方a1^2*q^8(1+

在等比数列｛an｝中,若a4*a7=32那么a5*a6=a4*a7=32又a5+a6=12解方程组得a5=4,a6=8或a5=8,a6=4①若a5=4,a6=8那么q=a6/a5=8/4=2所以a1=

你确定题目没问题?把a4改成a5就好算了!改了后,1,2,4,8,16,32,64,128..

a5的平方=a3*a7且a5与a3,a7同号所以a5=2倍根号2

解析a1q^2=1/2a1q^6=2所以q^4=4q=±√2a1=1/4a5=a1q^4=1/4x4=1

方法1：a7=a5*q^2(设q是公比）则q^2=a7/a5=3/2a9=a7×q^2=6*3/2=9方法2：a7*a7=a5*a9所以,a9=9

a5=4,a7=6,a5=a1*q^4=4a7=a1*q^6=6q^2=3/21.q=根号6/22.q=-根号6/2a1=9a1=9an=a1*q^(n-1)an=9*(根号6/2)^(n-1)an=

（1）a1(1+q^6)=65a1^2*q^6=64由a(n+1)

1、a7*a11=a4*a14=6,再加上a4+a14=5,可知a4=2,a14=3,q=(3/2)^1/10,a5/a16=(2/3)^9/10,答案全错2、b=1-a,代进去算就行了,我现在没时间

根据等比数列的性质相同间隔的数字同样可构成一个新的等比数列即如果有……a3a4a5a6a7……成等比数列则a3a5a7同样成等比数列所以a5的平方=a3xa7a5=2√2

a4=a3.a5a1r^3=(a1r^2)(a1r^4)r^3=8r^6r^3(8r^3-1)=0r=(1/2)a7=a1r^6=8(1/2)^6=1/8

a5(a3+2a5+a7)=a5a3+2a5a5+a5a7=a4a4+2a4a6+a6a6=(a4+a6)(a4+a6)=9

等比a3=a1q²a5=a3q²a7=a5q²所以(a3-a5+a7)/(a1-a3+a5)=q²=5/2同理aa9=a7q²所以(a5-a7+a9)

∵a3-a5+a7=(a1-a3+a5)q^2∴q^2=(a3-a5+a7)/(a1-a3+a5)=5/2∴a5-a7+a9=(a3-a5+a7)q^2=5×5/2=25/2