Cộng các phân số sau:
\(a)\,\,{{ – 2} \over 3} + {4 \over {15}};\,\,\,\,\,\,\,\,b)\,\,{{11} \over {15}} + {9 \over { – 10}};\,\,\,\,\,c)\,\,{1 \over { – 7}} + 3\)
Advertisements (Quảng cáo)
\(\eqalign{& a)\,\,{{ – 2} \over 3} + {4 \over {15}} = {{ – 2.5} \over {3.5}} + {4 \over {15}} = {{ – 10} \over {15}} + {4 \over {15}} = {{ – 10 + 4} \over {15}} = {{ – 6} \over {15}};\,\,\,\,\,\,\,\, \cr & b)\,\,{{11} \over {15}} + {9 \over { – 10}} = {{11.2} \over {15.2}} + {{9.( – 3)} \over { – 10.( – 3)}} = {{22} \over {30}} + {{ – 27} \over {30}} = {{22 + ( – 27)} \over {30}} = {{ – 5} \over {30}};\,\,\,\,\, \cr & c)\,\,{1 \over { – 7}} + 3 = {1 \over { – 7}} + {{ – 21} \over { – 7}} = {{1 + ( – 21)} \over { – 7}} = {{ – 20} \over { – 7}} = {{20} \over 7} \cr} \)