1. Thực hiện phép tính (tính nhanh nếu có thể): a) 1/5 -1/4 2. Tìm \[x\]: a) x - 2/5= - 2/3;
1.
a) \(\frac{1}{5} - \frac{1}{4}\; = \;\frac{4}{{20}} - \frac{5}{{20}}\; = \;\frac{{4 - 5}}{{20}}\; = \;\frac{{ - 1}}{{20}}\);
b) \(\frac{2}{{11}} - \frac{{11}}{8} + \frac{9}{{11}} + \frac{3}{8}\; = \;\frac{2}{{11}} + \frac{9}{{11}} + \left( { - \frac{{11}}{8} + \frac{3}{8}} \right) = 1 + ( - 1) = 0\).
2.
a) \(x - \frac{2}{5} = \frac{{ - 2}}{3}\) \(x = \frac{{ - 2}}{3} + \frac{2}{5}\) \(x = \frac{{ - 10}}{{15}} + \frac{6}{{15}}\) \(x = \frac{{ - 4}}{{15}}\) Vậy \(x = \frac{{ - 4}}{{15}}\). | b) \(27\,\,.\,\,{\left( {3x - \frac{1}{5}} \right)^3} = - 8\) \({\left( {3x - \frac{1}{5}} \right)^3} = - \frac{8}{{27}} = {\left( { - \frac{2}{3}} \right)^3}\) 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 \(x = - \frac{7}{{45}}\). |