a4 a7=5 a5a6=6 an

(1)由已知得：a2=2a1,a3=4a1,所以S3/a3=(a1+a2+a3)/a3=(a1+2a1+4a1)/(4a1)=7/4(2)这一步不知道要求什么结果,我就帮你求出an吧!由a5a6=81

∵在等比数列{an}中，a4+a7=2，a5a6=-8，∴a4+a7=2，且a4•a7=-8．故a4和a7是方程x2-2x-8=0的两个根，解得a4=4，a7=-2；或者a4=-2，a7=4．若a4=

/>a-5a+6a=0a-2a=3a-6a(a-2a)/(a-2a)=3设数列b=a-2a是公比为3等比数列,b1=a2-2a1=5-2*1=3b=3^na-5a+6a=0a-3a=2a-6a(a-3

在等比数列中有a5a6=a4a7=a3a8=a2a9=a1a10所以有log3a1+log3a2+...+log3a10=log3(a5a6*a4a7*a3a8*a2a9*a1a10)=5log3a5

a(n+1)/an=5^nan=a1*(a2/a1)(a3/a2)(a4/a3).(an/an-1)=4*5¹5²5³.*5^(n-1)=4*5^[1+2+3+……(n-

1.证：n≥2时,a(n+1)=5an-6a(n-1)a(n+1)-3an=2an-6a(n-1)=2[an-3a(n-1)][a(n+1)-3an]/[an-3a(n-1)]=2,为定值.a2-3a

1、设公比为qa4/q+a7*q=124a4*a7=-512设x=a4/q,y=a7*qx+y=124x*y=-512(x+y)^2=15376(x-y)^2=(x+y)^2-4xy=17424x-y

∵是各项为正数的等比数列{an}∴a5*a6=a1*a10=a2*a9=a3*a8=a4*a7∴log3a1+log3a2+log4a3+...log3a10=log3（a1*a2*a3*...*a1

设{an}公比为q.a5a6=(a4q)(a7/q)=a4a7=-8又a4+a7=2a4,a7是方程x²-2x-8=0的两根.x²-2x-8=0(x-4)(x+2)=0x=4或x=

设公比为q.数列是等比数列,则a4a7=a5a6=-8,又a4+a7=2,a4、a7是方程x²-2x-8=0的两根.(x-4)(x+2)=0x=4或x=-2以上就是x²-2x-8=

a（n+6）=an,就说明an的数值是不断周期性的重复的,重复的间隔就是6,从第i项ai开始,往后数6项,即第i+6项就和第i项的数字相等了.既然是6个一循环.那么100中有多少个6,就是经历了多少个

An=6Sn/(An+3)6Sn=(An)^2+3Ann>=26S(n-1)=(A(n-1))^2+3A(n-1)6An=(An)^2+3An-(A(n-1))^2-3A(n-1)(An)^2-(A(

1,a4+a7=a5+a6=5,而a5*a6=6所以a5=2,a6=3；或a5=3,a6=2当a5=2,a6=3时,d=a6-a5=1,此时an=a5+(n-5)d=2+n-5=n-3；当a5=3,a

由题意可得a5a6+a4a7=2a5a6=18，解得a5a6=9，∴log3a1+log3a2+…+log3a10=log3（a1a2…a10）=log3（a5a6）5=log395=log3310=

1、因为等比数列所以有a9/a6=a6/a3所以有a3=42、log1/2a1+log1/2a2+.+log1/2a10=log1/2(a1*a2*a3*a4*a5*a6*a7*a8*a9*a10)因

求∠A0OA1,∠A1OA2,∠A2OA3的大小∠A0OA1=arctan1=45°,∠A1OA2=arctan（1／√2）=35.26°,∠A2OA3=arctan（1／√3）=30°以此类推,,∠

∵等比数列{an}的各项均为正数，且a5a6＝13，∴a1a10=a2a9=a3a8=a4a7=a5a6＝13∴log3a1+log3a2+…+log3a10=log3a1a2…a10=log3(13

把通项表示为a[n],比较清楚a[n+1]=a[n]+6a[n-1]两边同时加上2a[n]变成：a[n+1]+2a[n]=3a[n]+6a[n-1]=3(a[n]+2a[n-1])两边同时减去3a[n

{an}是等比数列，∵a4a7=-512，a3+a8=124，∴a3a8=-512，a3+a8=124，∴a3和a8是方程x2-124x-512=0的两个实数根，解方程x2-124x-512=0，得x

10A5A6+A4A7=18(A1*q^4)*(A1*q^5)+(A1*q^3)*(A1*q^6)=18(A1^2)*(q^9)=9而log3A1+log3A2+…+log3A10=log3(A1*A