Đáp án:
$1)\\
a)
\dfrac{2}{15}\\
b)
1\\
c)
\dfrac{-13}{16}\\
d)
1\\
2)\\
a)
x=\dfrac{-30}{91}\\
b)
x=-2\\$
Giải thích các bước giải:
$1)\\
a)
\left ( \dfrac{-5}{24}+\dfrac{3}{4}-\dfrac{7}{12} \right ):\dfrac{-5}{16}\\
=\left ( \dfrac{-5}{24}+\dfrac{3.6}{24}-\dfrac{7.2}{24} \right ):\dfrac{-5}{16}\\
=\dfrac{-1}{24}.\dfrac{16}{-5}\\
=\dfrac{2}{15}\\$
$b)
\dfrac{7}{19}.\dfrac{8}{11}+\dfrac{7}{19}:\dfrac{11}{3}+\dfrac{12}{19}\\
=\dfrac{7}{19}.\dfrac{8}{11}+\dfrac{7}{19}.\dfrac{3}{11}+\dfrac{12}{19}\\
=\dfrac{7}{19}.\left (\dfrac{8}{11}+\dfrac{3}{11} \right )+\dfrac{12}{19}\\
=\dfrac{7}{19}.\dfrac{11}{11}+\dfrac{12}{19}\\
=\dfrac{19}{19}=1\\$
$c)
\left ( \dfrac{3}{8}-\dfrac{1}{4}+\dfrac{5}{12} \right ):\dfrac{-2}{3}\\
=\left ( \dfrac{9}{24}-\dfrac{6}{24}+\dfrac{10}{24} \right ):\dfrac{-2}{3}\\
=\dfrac{13}{24}.\dfrac{-3}{2}\\
=\dfrac{-13}{16}\\$
$d)
\dfrac{17}{13}.\dfrac{18}{23}-\dfrac{4}{13}:\dfrac{23}{18}+\dfrac{5}{23}\\
=\dfrac{17}{13}.\dfrac{18}{23}-\dfrac{4}{13}.\dfrac{18}{23}+\dfrac{5}{23}\\
=\dfrac{18}{13}.\dfrac{17}{23}-\dfrac{18}{13}.\dfrac{4}{23}+\dfrac{5}{23}\\
=\dfrac{18}{13}.\left (\dfrac{17}{23}-\dfrac{4}{23} \right )+\dfrac{5}{23}\\
=\dfrac{18}{13}.\dfrac{13}{23}+\dfrac{5}{23}\\
=\dfrac{18}{23}+\dfrac{5}{23}\\
=\dfrac{23}{23}=1\\
2)\\
a)
\dfrac{1}{3}-\dfrac{5}{7}:x=\dfrac{5}{2}\\
\Leftrightarrow \dfrac{5}{7}:x=\dfrac{1}{3}-\dfrac{5}{2}\\
\Leftrightarrow \dfrac{5}{7}:x=\dfrac{2}{6}-\dfrac{15}{6}\\
\Leftrightarrow \dfrac{5}{7}.\dfrac{1}{x}=\dfrac{-13}{6}\\
\Leftrightarrow \dfrac{1}{x}=\dfrac{-13}{6}.\dfrac{7}{5}\\
\Leftrightarrow \dfrac{1}{x}=\dfrac{-91}{30}\\
\Leftrightarrow x=\dfrac{-30}{91}\\
b)
\left ( \dfrac{4}{10}-x \right ):4=\dfrac{3}{5}\\
\Leftrightarrow \dfrac{2}{5}-x =\dfrac{3}{5}.4\\
\Leftrightarrow x=\dfrac{2}{5}-\dfrac{12}{5}\\
\Leftrightarrow x=\dfrac{-10}{5}=-2\\$
