(-1)+(+2)+(-3)+(+4)...+(-41)+(+42)=

来源：学生作业学帮网编辑：学帮网时间：2024/07/05 20:35:28

(-1)+(+2)+(-3)+(+4)...+(-41)+(+42)
=[(-1)+(+2)]+[(-3)+(+4)]...+[(-41)+(+42)]
=1*42/2
=21

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