2-1+3-2+4-3+……+50-49+51-50

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2-1+3-2+4-3+……+50-49+51-50
2-1+3-2+4-3+……+50-49+51-50

2-1+3-2+4-3+……+50-49+51-50
2-1+3-2+4-3+……+50-49+51-50
=(2-1)+(3-2)+.+(50-49)+(51-50)
=1+1+.+1
=1*50
=50

两个两个一组有50个-1