Thực hiện phép tính: (a) 14/15 − 4/15 . (b) − 5/18 − 3/12 + 7/9 .
Giải thích
a) \[\frac{{14}}{{15}} - \frac{4}{{15}}\]
\( = \frac{{10}}{{15}} = \frac{2}{3}.\)
b) \[\frac{{ - 5}}{{18}} - \frac{3}{{12}} + \frac{7}{9}\]
\[ = \frac{{ - 5}}{{18}} + \frac{7}{9} - \frac{1}{4}\]
\[ = \frac{{ - 5}}{{18}} + \frac{{14}}{{18}} - \frac{1}{4}\]
\[ = \frac{9}{{18}} - \frac{1}{4} = \frac{1}{2} - \frac{1}{4}\]
\( = \frac{1}{4}.\)
c) \[\frac{{ - 9}}{{28}} \cdot \frac{{35}}{{18}} + \frac{5}{{32}}:\frac{{15}}{{12}}\]
\( = \frac{{ - 1}}{4} \cdot \frac{5}{2} + \frac{5}{{32}} \cdot \frac{{12}}{{15}}\)
\( = \frac{{ - 5}}{8} + \frac{5}{{32}} \cdot \frac{4}{5}\)
\( = \frac{{ - 5}}{8} + \frac{1}{8} = \frac{{ - 4}}{8} = \frac{{ - 1}}{2}.\)