已知前n项和公式,求公比q答:通项公式 an=a1*q^(n-1)(即q的n-1次方) a1为首项,an为第n项 an=a1*q^(n-1,am=a1*q^(m-1))则an/am=q^(n-m)(1)an=am*q^(n-m)(2)a,G,b 若构成等比中项,则G^2=ab (a,b,G不等于0)(3)若m+n=p+q 则 am*an=ap+aq 2.等比数列前n项和{an} 设 a1,a2,a3...
等比数列的前n项和公式?答:⑶若数列为等差数列,则S n,S2n -Sn ,S3n -S 2n,…仍然成等差数列,公差为k^2d .(4)若数列{an}与{bn}均为等差数列,且前n项和分别是Sn和Tn,则am/bm=S2m-1/T2m-1.⑸在等差数列中,S = a,S = b (n>m),则S = (a-b).2. 等比数列前N项和公式:Sn代表项数之和,n代表...