1-1/2-5/6+7/20-9/20+11/30-13/42怎么算
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1-1/2-5/6+7/20-9/20+11/30-13/42怎么算
解:
1-1/2-5/6+7/20-9/20+11/30-13/42
=1-1/2-(1/2+1/3)-1/10+(1/5+1/6)-(1/6+1/7)
=1-1/2-1/2-1/3-1/10+1/5+1/6-1/6-1/7
=-1/3+1/10-1/7
=-79/120
题目打错,应该是这个:
1-1/2-5/6+7/12-9/20+11/30-13/42
=1/2-(1/2+1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)
=1/2-1/2-1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7
=-1/7
解:
1-1/2-5/6+7/20-9/20+11/30-13/42
=1-1/2-(1/2+1/3)-1/10+(1/5+1/6)-(1/6+1/7)
=1-1/2-1/2-1/3-1/10+1/5+1/6-1/6-1/7
=-1/3+1/10-1/7
=-79/120
题目打错,应该是这个:
1-1/2-5/6+7/12-9/20+11/30-13/42
=1/2-(1/2+1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)
=1/2-1/2-1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7
=-1/7
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