1. Thực hiện phép tính (tính nhanh nếu có thể): a) 3/5 - 2/5.10/12; 2. Tìm x: a)- 7/9x = 3(1/2);
1.
a) \[\frac{3}{5} - \frac{2}{5}.\frac{{10}}{{12}}\]\[ = \frac{3}{5} - \frac{1}{3}\]\[ = \frac{9}{{15}} - \frac{5}{{15}} = \frac{4}{{15}}\];
b) \[\frac{2}{{{{\left( { - 3} \right)}^2}}} + \frac{5}{{ - 12}} - \frac{{ - 3}}{4}\]\[ = \frac{2}{9} + \frac{{ - 5}}{{12}} + \frac{3}{4}\]
\[ = \frac{8}{{36}} + \frac{{ - 15}}{{36}} + \frac{{27}}{{36}}\]\[ = \frac{{20}}{{36}}\]\[ = \frac{5}{9}\].
2.
a) \[\frac{{ - 7}}{9}x = 3\frac{1}{2}\] \[\frac{{ - 7}}{9}x = \frac{7}{2}\] \[x = \frac{7}{2}:\left( {\frac{{ - 7}}{9}} \right)\] \[x = \frac{{ - 9}}{2}\] Vậy \[x = \frac{{ - 9}}{2}\].
| b) \[\frac{3}{5}\left( {x + \frac{{11}}{2}} \right) = 0,4\] \[\frac{3}{5}\left( {x + \frac{{11}}{2}} \right) = \frac{2}{5}\] \[x + \frac{{11}}{2} = \frac{2}{5}:\frac{3}{5}\] \[x + \frac{{11}}{2} = \frac{2}{3}\] \[x = \frac{2}{3} - \frac{{11}}{2}\] \[x = \frac{{ - 29}}{6}\] Vậy \[x = \frac{{ - 29}}{6}\]. |