Bài 59 trang 33 SGK Toán 6 Tập 2

Đề bài

Tính:

a) $\dfrac{1}{8}-\dfrac{1}{2}$ ;               b) $\dfrac{-11}{12}-(-1)$ ;            c) $\dfrac{3}{5}-\dfrac{5}{6}$ ;

d) $\dfrac{-1}{16}-\dfrac{1}{15}$            e) $\dfrac{11}{36}-\dfrac{-7}{24}$ ;                  g) $\dfrac{-5}{9}-\dfrac{-5}{12}.$ 

Lời giải chi tiết

a) $\dfrac{1}{8}-\dfrac{1}{2}=\dfrac{1}{8}+\left (-\dfrac{1}{2} \right )$$=\dfrac{1}{8}+\dfrac{-4}{8}=\dfrac{-3}{8}$.

b) $\dfrac{-11}{12}-(-1)=\dfrac{-11}{12}-\left (-\dfrac{12}{12} \right )$$=\dfrac{-11}{12}+\dfrac{12}{12}=\dfrac{1}{12}.$

c) $\dfrac{3}{5}-\dfrac{5}{6}=\dfrac{3}{5}+\left (-\dfrac{5}{6} \right )$$=\dfrac{{18}}{{30}} + \left( {\dfrac{{ - 25}}{{30}}} \right)=\dfrac{18+(-25)}{30}=\dfrac{-7}{30}.$

d)  $\dfrac{{ - 1}}{{16}} - \dfrac{1}{{15}} = \dfrac{{ - 1}}{{16}} + \left( { - \dfrac{1}{{15}}} \right)$$= \dfrac{{ - 15}}{{240}} + \left( { - \dfrac{{16}}{{240}}} \right)$$= \dfrac{{ - 31}}{{240}}$

e) $\dfrac{{11}}{{36}} - \dfrac{{ - 7}}{{24}}$$= \dfrac{{11}}{{36}} + \dfrac{7}{{24}}$$= \dfrac{{22}}{{72}} + \dfrac{{21}}{{72}}$$= \dfrac{{43}}{{72}}$                    

g) $\dfrac{{ - 5}}{9} - \dfrac{{ - 5}}{{12}} = \dfrac{{ - 5}}{9} + \dfrac{5}{{12}}$$= \dfrac{{ - 20}}{{36}} + \dfrac{{15}}{{36}} = \dfrac{-5}{{36}}$

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