2*(1/2)+5+9*(1/2)+18+34*(1/2)+67+...的前n项和

Question

2*(1/2)+5+9*(1/2)+18+34*(1/2)+67+...的前n项和

Answer 1

a1=5/2 a2=10/2=(5*2-0)/2a3=19/2=(10*2-1)/2a4=36/2=(19*2-2)/2a5=69/2=(36*2-3)/2a6=134/2=(69*2-4)/2……an=2a(n-1)-(n-2)/2化为：an-n/2=2[a(n-1)-(n-1)/2]所以数列{an-n/2}为首项为2,公比为2的等比数列则an-n/2...