计算1/5+1/10+1/20+1/40+…+1/2560

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计算1/5+1/10+1/20+1/40+…+1/2560计算1/5+1/10+1/20+1/40+…+1/2560计算1/5+1/10+1/20+1/40+…+1/25601/5+1/10+1/20

计算1/5+1/10+1/20+1/40+…+1/2560
计算1/5+1/10+1/20+1/40+…+1/2560

计算1/5+1/10+1/20+1/40+…+1/2560
1/5+1/10+1/20+1/40+…+1/2560
= 1/2560 * (512 + 256 + 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1)
= 1/2560 * (2^9 + 2^8 + ... + 2^0)
= 1/2560 * (2^10 - 1)
= 1/2560 * (1024 - 1)
= 1023/2560

这是等比数列,公比1/10/(1/5)=1/2
Sn=(1/5-1/2560*1/2)/(1-1/2)
=(1/5-1/5120)/(1/2)
=2/5-1/2560
=(2*512-1)/2560
=1023/2560
Sn=(A1-An*q)/(1-q)
Sn前n项和
A1首项,An第n项
q公比