两个等差数列{an},(bn}前n项和分别为Sn,S'n,若Sn/S'n=(2n+3)/(3n-1)求a9/b9_数学解答

两个等差数列{an},(bn}前n项和分别为Sn,S'n,若Sn/S'n=(2n+3)/(3n-1)求a9/b9

人气：232 ℃　时间：2020-02-05 12:40:46

解答

an=a+(n-1)dbn=b+(n-1)c则Sn=(2a+nd-d)*n/2S'n=(2b+cn-c)*n/2Sn/S'n=[2a+(n-1)d]/[2b+(n-1)c]=(2n+3)/(3n-1)a9/b9=(a+8d)/(b+8c)=(2a+16d)/(2a+16c)则(2a+16d)/(2a+16c)就是n=17时[2a+(n-1)d]/[2b+(n-1)c]的值n=17,[...