Question

2014长宁区数学文科一模卷第五题

Answer 1

设an/2^n = bn,则b1+b2+.+bn=2n+5,b1+b2+...+bn-1 = 2n+3; so bn=2=an/2^n; so an = 2^(n+1);

此外,n=1时,an=14；

so an=2^(n+1),n不为1；an=14,n=1