Đáp án:
$a) \dfrac{-49}{60}\\
b)
\dfrac{1}{7}\\
c)
\dfrac{-2}{7}\\
d)
\dfrac{907}{1840}$
Giải thích các bước giải:
$a) \dfrac{1}{3}:\dfrac{-4}{5}+\dfrac{1}{3}.\dfrac{-6}{5}\\
=\dfrac{1}{3}.\dfrac{-5}{4}+\dfrac{1}{3}.\dfrac{-6}{5}\\
=\dfrac{1}{3}.\left ( \dfrac{-5}{4}-\dfrac{6}{5} \right )\\
=\dfrac{1}{3}.\left ( \dfrac{-25}{20}-\dfrac{24}{20} \right )\\
=\dfrac{1}{3}.\dfrac{-49}{20}\\
=\dfrac{-49}{60}\\
b)
\dfrac{3}{7}.\dfrac{9}{26}-\dfrac{1}{14}.\dfrac{1}{13}\\
=\dfrac{3}{7}.\dfrac{9}{13.2}-\dfrac{1}{14}.\dfrac{1}{13}\\
=\dfrac{1}{13}.\left ( \dfrac{27}{14}-\dfrac{1}{14} \right )\\
=\dfrac{1}{13}.\dfrac{26}{14}\\
=\dfrac{1}{7}\\
c)
\dfrac{1}{7}.\left ( -\dfrac{3}{8} \right )+\dfrac{1}{7}.\left ( -\dfrac{13}{8} \right )\\
=\dfrac{1}{7}.\left ( -\dfrac{3}{8}-\dfrac{13}{8} \right )\\
=\dfrac{1}{7}.\dfrac{-16}{8}\\
=\dfrac{-2}{7}\\
d)
\dfrac{3}{5}.\dfrac{15}{16}-\dfrac{1}{10}.\dfrac{16}{23}\\
=\dfrac{3}{1}.\dfrac{3}{16}-\dfrac{1}{5}.\dfrac{8}{23}\\
=\dfrac{9}{16}-\dfrac{8}{115}\\
=\dfrac{1035}{1840}-\dfrac{128}{1840}\\
=\dfrac{907}{1840}$
