1. Thực hiện phép tính (tính nhanh nếu có thể): a) 1/5-1/4; 2. Tìm \[x\]: a) (- 7/9)x = 3(1/2);
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) \[\frac{{ - 7}}{9}x = 3\frac{1}{2}\] \[\frac{{ - 7}}{9}x = \frac{7}{2}\] \[x = \frac{7}{2}:\left( {\frac{{ - 7}}{9}} \right)\] \[x = \frac{{ - 9}}{2}\] 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 \[x = \frac{{ - 29}}{6}\]. |