1. Thực hiện phép tính (tính nhanh nếu có thể): a) 5/7 +4/- 14; 2. Tìm x: a) x -2/5= - 2/3
1.
a) \[\frac{5}{7} + \frac{4}{{ - 14}}\]\[ = \frac{5}{7} + \frac{{ - 2}}{7}\]\[ = \frac{3}{7}\];
b) \(\frac{2}{{11}}.\frac{{ - 5}}{4} + \frac{{ - 9}}{{11}}.\frac{5}{4} + 1\frac{3}{4}\)\( = \frac{2}{{11}}.\frac{{ - 5}}{4} + \frac{9}{{11}}.\frac{{ - 5}}{4} + \frac{7}{4}\)
\( = \frac{{ - 5}}{4}.\left( {\frac{2}{{11}} + \frac{9}{{11}}} \right) + \frac{7}{4}\)\( = \frac{{ - 5}}{4}.1 + \frac{7}{4}\)
\[ = \frac{5}{4} + \frac{7}{4}\]\[ = \frac{{12}}{4} = 3\].
2.
\(x - \frac{2}{5} = \frac{{ - 2}}{3}\) \(x = \frac{{ - 2}}{3} + \frac{2}{5}\) \(x = \frac{{ - 10}}{{15}} + \frac{6}{{15}}\) \(x = \frac{{ - 4}}{{15}}\) Vậy \(x = \frac{{ - 4}}{{15}}\). | \(27{\left( {3x - \frac{1}{5}} \right)^3} = - 8\) \({\left( {3x - \frac{1}{5}} \right)^3} = - \frac{8}{{27}} = {\left( { - \frac{2}{3}} \right)^3}\) Suy ra \(3x - \frac{1}{5} = - \frac{2}{3}\) \(3x = - \frac{2}{3} + \frac{1}{5}\) \(3x = - \frac{7}{{15}}\) \(x = - \frac{7}{{45}}\) Vậy \(x = - \frac{7}{{45}}\). |