两等差数列{an}和{bn},前n项和分别为Sn,Tn,且SnTn=7n+2n+ 发布时间:2017-04-29 14:55 │ 来源:www.tikuol.com 题型:填空题 问题: 两等差数列{an}和{bn},前n项和分别为Sn,Tn,且SnTn=7n+2n+3,则a2+a20b7+b15=______.