Advertisements (Quảng cáo)
So sánh các phân số:
\(a)\,\,{{ – 11} \over {12}}\,\,\,\& \,\,\,{{17} \over { – 18}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,b)\,\,{{ – 14} \over {21}}\,\,\,\& \,\,\,{{ – 60} \over { – 72}}\)
a)
12 = 22.3
-18 = 2. 3. (-3)
Suy ra BCNN(12, -18) = 22.32 = 36
Advertisements (Quảng cáo)
\(\eqalign{& {{ – 11} \over {12}} = {{ – 11.3} \over {12.3}} = {{ – 33} \over {36}} \cr & {{17} \over { – 18}} = {{17.( – 2)} \over { – 18.( – 2)}} = {{ – 34} \over {36}} \cr & {{ – 33} \over {36}} > {{ – 34} \over {36}} \cr & \Rightarrow {{ – 11} \over {12}} < {{17} \over { – 18}} \cr} \)
b)
21 = 3 . 7
-72 = 23.3 (-3)
Suy ra BCNN(21, -72) = 23.32.7 = 504
\(\eqalign{& {{ – 14} \over {21}} = {{ – 14.24} \over {21.24}} = {{ – 336} \over {504}} \cr & {{ – 60} \over { – 72}} = {{ – 60.( – 7)} \over { – 72.( – 7)}} = {{4200} \over {504}} \cr & {{ – 336} \over {504}} < {{420} \over {504}} \cr & \Rightarrow {{ – 14} \over {21}} < {{ – 60} \over { – 72}} \cr} \)