Thực hiện phép tính. (a) 11/7 + − 5/21 . (b) 5/17 − 25/31 + 12/17 + − 6/31 .
Giải thích
a) \[\frac{{11}}{7} + \frac{{ - 5}}{{21}} = \frac{{33}}{{21}} + \frac{{ - 5}}{{21}}\]\[ = \frac{{28}}{{21}} = \frac{4}{3}\].
b) \[\frac{5}{{17}} - \frac{{25}}{{31}} + \frac{{12}}{{17}} + \frac{{ - 6}}{{31}} = \left( {\frac{5}{{17}} + \frac{{12}}{{17}}} \right) - \left( {\frac{{25}}{{31}} + \frac{6}{{31}}} \right)\]\[ = 1 - 1 = 0\].