数列﹛an﹜前n项和sn=(3-1)+(3²-1)+(3³-1)+…+(3^n -1),求s10的值?
问题描述:
数列﹛an﹜前n项和sn=(3-1)+(3²-1)+(3³-1)+…+(3^n -1),求s10的值?
答
sn=(3-1)+(3²-1)+(3³-1)+…+(3^n -1)
所以
s10=(3-1)+(3²-1)+(3³-1)+…+(3^10 -1)
=(3+3²+3³+…+3^10) -1*10
=3*(1-3^10)/(1-3)-10
=3/2*(3^10-1)-10
=88572-10
=88562