等比数列:1/4+1/8+```+1/2的n次方,怎样求Sn?
问题描述:
等比数列:1/4+1/8+```+1/2的n次方,怎样求Sn?
答
错位相减呀
设这个数列为Sn
则 (1/2)Sn = 1/8+1/16+```+1/2^n+1/2^(n+1)
然后两个式子相减
会了吧?
我写完整