2a(3)—拦举a(7)^2+2a(11)=04a(7)-a(7)^2=0a(7)=4 或a(7)=0 (碰猛舍去笑衡桥)b(7)=a(7)=4log(2)(b6*b8)=log(2)(b(7)^2)=2log(2)(b(7))=4