已知数列an等于负一的n次方乘n,求前2016项的和s2016

2025-01-19 20:20:59
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回答1:

an = (-1)^n .n
Sn = a1+a2+...+an
S2016= -1+2 -3+4+...-2015+2016
=(-1+2) -(3+4)+...+(-2015+2016)
=1+1+...+1
=1008