(-1)+(+2)+(-3)+(+4)+...+(-41)+(+42)最后等于多少?

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(-1)+(+2)+(-3)+(+4)+...+(-41)+(+42)最后等于多少?
(-1)+(+2)+(-3)+(+4)+...+(-41)+(+42)最后等于多少?

(-1)+(+2)+(-3)+(+4)+...+(-41)+(+42)最后等于多少?
(-1)+(+2)+(-3)+(+4)+...+(-41)+(+42) =(-1+20)+(-3+4)+...+(-41+42) =1+1+...+1 =21

1 2 3 4 1 2 3 4 1 2 3 4 1,2,3,4, 1 2 3 4 1 2 3 4 1,2,3,4, 1,2,3,4, 1,2,3,4, 1,2,3,4, 1 2 3 4 1,2,3,4, 1,2,3,4, 1,2,3,4, 1、2、3、4 1+2+3×4 1,2,3,4 1+2+3+4+.