Đề bài

Tính a) \(\dfrac{3}{5} - \dfrac{{ - 1}}{3}\) b) \( - 3 - \dfrac{2}{7}\)

Lời giải chi tiết

a) \(\dfrac{3}{5} - \dfrac{{ - 1}}{3}\)\( = \dfrac{{3.3}}{{5.3}} - \dfrac{{ - 1.5}}{{3.5}}\)\( = \dfrac{9}{{15}} - \dfrac{{ - 5}}{{15}} = \dfrac{{9 - \left( { - 5} \right)}}{{15}} = \dfrac{{14}}{{15}}\)b) \( - 3 - \dfrac{2}{7}\)\(\begin{array}{l} = \dfrac{{ - 3.7}}{{1.7}} - \dfrac{2}{7}\\ = \dfrac{{ - 21}}{7} - \dfrac{2}{7}\\ = \dfrac{{ - 21 - 2}}{7}\\ = \dfrac{{ - 23}}{7}\end{array}\)