Advertisements (Quảng cáo)
Thực hiện phép tính và so sánh các kết quả tìm được :
a) \({4 \over 7}.{2 \over 5}\) với \({{ – 2} \over 5}.{4 \over 7}\)
b) \(\left( {{{ – 5} \over {12}}.{6 \over {11}}} \right).{{22} \over 9}\) với \({{ – 5} \over {12}}.\left( {{6 \over {11}}.{{22} \over 9}} \right)\)
c) \({{ – 2} \over 5}.\left( {{3 \over 4} + {1 \over 2}} \right)\) với \({{ – 2} \over 5}.{3 \over 4} + {{ – 2} \over 5}.{1 \over 2}\)
\(\eqalign{ & a){4 \over 7}.{{ – 2} \over 5} = {{4.( – 2)} \over {7.5}} = {{ – 8} \over {35}}; \cr & {{ – 2} \over 5}.{4 \over 7} = {{ – 2.4} \over {5.7}} = {{ – 8} \over {35}}. \cr} \)
Advertisements (Quảng cáo)
Vậy \({4 \over 7}.{{ – 2} \over 5} = {{ – 2} \over 5}.{4 \over 7}\)
\(\eqalign{ & b)\left( {{{ – 5} \over {12}}.{6 \over {11}}} \right).{{22} \over 9} = \left( {{{ – 5.6} \over {12.11}}} \right).{{22} \over 9} = \left( {{{ – 5.1} \over {2.11}}} \right).{{22} \over 9} = {{ – 5.22} \over {22.9}} = {{ – 5.1} \over {22.9}} = {{ – 5.1} \over {1.9}} = {{ – 5} \over 9} \cr & {{ – 5} \over {12}}.\left( {{6 \over {11}}.{{22} \over 9}} \right) = {{ – 5} \over {12}}.\left( {{{6.22} \over {11.9}}} \right) = {{ – 5} \over {12}}.\left( {{{2.2} \over {1.3}}} \right) = {{ – 5} \over {12}}.{4 \over 3} = {{ – 5.4} \over {12.3}} = {{ – 5.1} \over {3.3}} = {{ – 5} \over 9} \cr} \)
Vậy \(\left( {{{ – 5} \over {12}}.{6 \over {11}}} \right).{{22} \over 9} = {{ – 5} \over {12}}.\left( {{6 \over {11}}.{{22} \over 9}} \right).\)
\(\eqalign{ & c){{ – 2} \over 5}.\left( {{3 \over 4} + {1 \over 2}} \right) = {{ – 2} \over 5}.\left( {{3 \over 4} + {2 \over 4}} \right) = {{ – 2} \over 5}.{5 \over 4} = {{ – 2.5} \over {5.4}} = {{ – 1} \over 2} \cr & {{ – 2} \over 5}.{3 \over 4} + {{ – 2} \over 5}.{1 \over 2} = {{ – 2.3} \over {5.4}} + {{ – 2.1} \over {5.2}} = {{ – 3} \over {10}} + {{ – 2} \over {10}} = {{ – 1} \over 2}. \cr} \)
Vậy \({{ – 2} \over 5}.\left( {{3 \over 4} + {1 \over 2}} \right) = {{ – 2} \over 5}.{3 \over 4} + {{ – 2} \over 5}.{1 \over 2}\)