a) Ta có:
\(\begin{array}{l}\dfrac{1}{4} - \dfrac{1}{6} = \dfrac{3}{{12}} - \dfrac{2}{{12}} = \dfrac{1}{{12}}\\\dfrac{1}{{30}} + \dfrac{1}{{12}} = \dfrac{2}{{60}} + \dfrac{5}{{60}} = \dfrac{7}{{60}}\\\dfrac{7}{{60}} + \dfrac{1}{4} = \dfrac{7}{{60}} + \dfrac{{15}}{{60}} = \dfrac{{22}}{{60}} = \dfrac{{11}}{{30}}\\\dfrac{{11}}{{30}} + \dfrac{1}{5} = \dfrac{{11}}{{30}} + \dfrac{6}{{30}} = \dfrac{{17}}{{30}}\\\dfrac{{ - 7}}{{60}} + \dfrac{1}{5} = \dfrac{{ - 7}}{{60}} + \dfrac{{12}}{{60}} = \dfrac{5}{{60}} = \dfrac{1}{{12}}\\\dfrac{1}{{12}} + \dfrac{{17}}{{30}} = \dfrac{5}{{60}} + \dfrac{{34}}{{60}} = \dfrac{{39}}{{60}} = \dfrac{{13}}{{20}}\\\dfrac{1}{5} - \dfrac{7}{{60}} = \dfrac{{12}}{{60}} - \dfrac{7}{{60}} = \dfrac{5}{{60}} = \dfrac{1}{{12}}\\\dfrac{{ - 7}}{{60}} - \dfrac{1}{{12}} = \dfrac{{ - 7}}{{60}} + \dfrac{{ - 5}}{{60}} = \dfrac{{ - 12}}{{60}} = \dfrac{{ - 1}}{5}\\\dfrac{1}{{12}} - \dfrac{1}{{30}} = \dfrac{5}{{60}} - \dfrac{2}{{60}} = \dfrac{3}{{60}} = \dfrac{1}{{20}}\\\dfrac{{ - 1}}{5} - \dfrac{1}{{20}} = \dfrac{{ - 4}}{{20}} + \dfrac{{ - 1}}{{20}} = \dfrac{{ - 5}}{{20}} = \dfrac{{ - 1}}{4}\end{array}\)
Ta điền các số như sau:
b)
\(\begin{array}{l}\dfrac{{ - 1}}{2}.\dfrac{2}{3} = \dfrac{{ - 1}}{3}\\\dfrac{2}{3}.\dfrac{3}{4} = \dfrac{1}{2}\\\dfrac{{ - 1}}{3}.\dfrac{1}{2} = \dfrac{{ - 1}}{6}\\\dfrac{1}{3}.\dfrac{{ - 1}}{6} = \dfrac{{ - 1}}{{18}}\\\dfrac{{ - 1}}{6}.\left( { - 1} \right) = \dfrac{1}{6}\\\dfrac{{ - 1}}{{18}}.\dfrac{1}{6} = \dfrac{{ - 1}}{{108}}\\\dfrac{1}{3}:\dfrac{{ - 1}}{3} = \dfrac{1}{3}.\dfrac{{ - 3}}{1} = - 1\\\left( { - 1} \right):\dfrac{1}{2} = \left( { - 1} \right).\dfrac{2}{1} = \left( { - 2} \right)\\\left( { - 1} \right):\dfrac{{ - 1}}{2} = \left( { - 1} \right).\dfrac{{ - 2}}{1} = 2\\\left( { - 2} \right):\dfrac{3}{4} = \left( { - 2} \right).\dfrac{4}{3} = \dfrac{{ - 8}}{3}\end{array}\)
Ta điền như sau:
