So sánh các số hữu tỉ sau bằng cách nhanh nhất:
a) \({\rm{}}{{ – 1} \over 5} < {1 \over {1000}}\)
b) \({{267} \over { – 268}} > {{ – 1347} \over {1343}}\)
c) \({{ – 13} \over {38}} < {{29} \over { – 88}}\)
d) \({\rm{}}{{ – 18} \over {31}} = {{ – 181818} \over {313131}}\)
\({\rm{a}}.{{ – 1} \over 5} < {0 \over {5}} = 0;{1 \over {1000}} > {0 \over {1000}} = 0\)
Vậy \({{ – 1} \over 5} < {1 \over {1000}}\)
b) \({{267} \over { – 268}} = {{ – 267} \over {268}} > {{ – 268} \over {268}} = – 1;\)
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\({{ – 1347} \over {1343}} < {{ – 1343} \over {1343}} = – 1\)
Vậy \({{267} \over { – 268}} > {{ – 1347} \over {1343}}\)
c) \({{ – 13} \over {38}} < {{-13} \over { – 39}} = {{ – 1} \over 3};{{29} \over { – 88}} = {{ – 29} \over {88}} > {{ – 29} \over {87}} = {{ – 1} \over 3}\)
Vậy \({{ – 13} \over {38}} < {{29} \over { – 88}}\)
d) \({\rm{}}{{ – 18} \over {31}} = {{ – 18.10101} \over {31.10101}} = {{ – 181818} \over {313131}}\)
Vậy \({\rm{}}{{ – 18} \over {31}} = {{ – 181818} \over {313131}}\)