a) 5/15 + 14/25 – 12/9 + 2/7 + 11/25 =? b) 15 × 1/5 : ( -5/7) – 2 trên 1/5 × ( -7/5 )=?

0 bình luận về “a) 5/15 + 14/25 – 12/9 + 2/7 + 11/25 =? b) 15 × 1/5 : ( -5/7) – 2 trên 1/5 × ( -7/5 )=?”

1. Đáp án:

   a. \(\dfrac{2}{7}\)

   Giải thích các bước giải:

   \(\begin{array}{l}
   a.\dfrac{5}{{15}} + \dfrac{{14}}{{25}} – \dfrac{{12}}{9} + \dfrac{2}{7} + \dfrac{{11}}{{25}}\\
    = \dfrac{1}{3} + \dfrac{{14}}{{25}} – \dfrac{4}{3} + \dfrac{2}{7} + \dfrac{{11}}{{25}}\\
    = \left( {\dfrac{1}{3} – \dfrac{4}{3}} \right) + \left( {\dfrac{{14}}{{25}} + \dfrac{{11}}{{25}}} \right) + \dfrac{2}{7}\\
    =  – 1 + 1 + \dfrac{2}{7} = \dfrac{2}{7}\\
   b.\dfrac{{15.\dfrac{1}{5}:\left( { – \dfrac{5}{7}} \right) – 2}}{{\dfrac{1}{5}.\left( { – \dfrac{7}{5}} \right)}}\\
    = \dfrac{{3.\left( { – \dfrac{7}{5}} \right) – 2}}{{\dfrac{1}{5}.\left( { – \dfrac{7}{5}} \right)}}\\
    = \left( { – \dfrac{{21}}{5} – 2} \right):\left( { – \dfrac{7}{{25}}} \right)\\
    =  – \dfrac{{31}}{5}.\left( { – \dfrac{{25}}{7}} \right) = \dfrac{{31.5}}{7} = \dfrac{{155}}{7}
   \end{array}\)

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2. ${a,}$ $\dfrac{5}{15}+$ $\dfrac{14}{25}-$ $\dfrac{12}{9}+$ $\dfrac{2}{7}+$ $\dfrac{11}{25}$

   ${=}$ $\dfrac{1}{3}+$ $\dfrac{14}{25}-$ $\dfrac{4}{3}+$ $\dfrac{2}{7}+$ $\dfrac{11}{25}$

   ${=}$ $(\dfrac{1}{3}-$ $\dfrac{4}{3})+$ $(\dfrac{14}{25}+$ $\dfrac{11}{25})+$ $\dfrac{2}{7}$

   ${=-1+1+}$ $\dfrac{2}{7}$

   ${=}$ $\dfrac{2}{7}$

   ${b,15}$ x $\dfrac{1}{5}:$ $(-\dfrac{5}{7})-$ $\dfrac{2}{15}$ x $(-\dfrac{7}{5})$

   ${=}$ $-\dfrac{21}{5}-$ $(-\dfrac{14}{75})$

   $=-\dfrac{315}{75}-$ $(-\dfrac{14}{75})$

   ${=}$ $-\dfrac{301}{75}$

    ~Xin hay nhất~

    

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