数列1,-5,9,-13,17,-21,(-1)^n-1(4n-3),求s15

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数列1,-5,9,-13,17,-21,(-1)^n-1(4n-3),求s15数列1,-5,9,-13,17,-21,(-1)^n-1(4n-3),求s15数列1,-5,9,-13,17,-21,(-

数列1,-5,9,-13,17,-21,(-1)^n-1(4n-3),求s15
数列1,-5,9,-13,17,-21,(-1)^n-1(4n-3),
求s15

数列1,-5,9,-13,17,-21,(-1)^n-1(4n-3),求s15
a15=(-1)^15-1(4*15-3)=57
S14=(1-5)+(9-13)...=7*(-4)=-28
S15=S14+a15=-28+57=29