Đáp án:
$1)
a)\dfrac{-163}{180}\\
b)
\dfrac{-17}{9}\\
c)
\dfrac{-4847}{4875}\\
2)
a)
x=\dfrac{-7}{12}\\
b)
x=\dfrac{251}{58}\\$
Giải thích các bước giải:
$1)
a)\dfrac{-17}{30}-\dfrac{11}{-45}+\dfrac{-7}{12}\\
=\dfrac{-17}{30}+\dfrac{11}{45}+\dfrac{-7}{12}\\
=\dfrac{-17.6}{180}+\dfrac{11.4}{180}+\dfrac{-7.15}{180}\\
=\dfrac{-163}{180}\\
b)
-\dfrac{5}{9}+\dfrac{5}{9}:\left ( 1\dfrac{2}{3}-2\dfrac{1}{12} \right )\\
=-\dfrac{5}{9}+\dfrac{5}{9}:\left ( \dfrac{5}{3}-\dfrac{25}{12} \right )\\
=-\dfrac{5}{9}+\dfrac{5}{9}:\left ( \dfrac{20}{12}-\dfrac{25}{12} \right )\\
=-\dfrac{5}{9}+\dfrac{5}{9}:\dfrac{-5}{12}\\
=-\dfrac{5}{9}+\dfrac{5}{9}.\dfrac{-12}{5}\\
=-\dfrac{5}{9}+\dfrac{-4}{3}\\
=-\dfrac{5}{9}+\dfrac{-12}{9}\\
=\dfrac{-17}{9}\\
c)
\dfrac{-7}{25}.\dfrac{11}{13}+\dfrac{-7}{25}.\dfrac{2}{15}-\dfrac{18}{25}\\
=\dfrac{-7}{25}.\left (\dfrac{11}{13}+\dfrac{2}{15}+\dfrac{18}{7} \right )\\
=\dfrac{-7}{25}.\left (\dfrac{11.105}{1365}+\dfrac{2.91}{1365}+\dfrac{18.195}{1365} \right )\\
=\dfrac{-7}{25}.\dfrac{4847}{1365}\\
=\dfrac{-4847}{4875}\\
2)
a)
x+\dfrac{-7}{15}=-1\dfrac{1}{20}\\
\Leftrightarrow x=\dfrac{-21}{20}+\dfrac{7}{15}\\
\Leftrightarrow x=\dfrac{-21.3}{60}+\dfrac{28}{60}\\
\Leftrightarrow x=\dfrac{-35}{60}=\dfrac{-7}{12}\\
b)
\left ( 3\dfrac{1}{2}-x \right ).1\dfrac{1}{4}=-1\dfrac{1}{29}\\
\Leftrightarrow \left ( \dfrac{7}{2}-x \right ).\dfrac{5}{4}=\dfrac{-30}{29}\\
\Leftrightarrow \dfrac{7}{2}-x=\dfrac{-30}{29}.\dfrac{4}{5}=\dfrac{-24}{29}\\
\Leftrightarrow x=\dfrac{7}{2}+\dfrac{24}{29}\\
\Leftrightarrow x=\dfrac{7.29}{58}+\dfrac{24.2}{58}\\
\Leftrightarrow x=\dfrac{251}{58}\\$
