Đáp án:

 $1) a)\dfrac{-5}{12}\\
b)\dfrac{-17}{9}\\
c)-1\\
2)
a)x=\dfrac{-7}{12}\\
b)x=\dfrac{217}{50}\\
c) x=\dfrac{2}{5}$

Giải thích các bước giải:

$1) a)\dfrac{-17}{30}-\dfrac{11}{-15}+\dfrac{-7}{12}=\dfrac{(-17).2}{60}+\dfrac{11.4}{60}-\dfrac{7.5}{60}\\
=\dfrac{-34+44-35}{60}=\dfrac{-25}{60}=\dfrac{-5}{12}\\
b)\dfrac{-5}{9}+\dfrac{5}{9}:\left ( 1\dfrac{2}{3}-2\dfrac{1}{12} \right )=\dfrac{5}{9}\left ( -1+1:\left [ \dfrac{5}{3}-\dfrac{25}{12} \right ] \right )\\
=\dfrac{5}{9}\left ( -1+1:\left [ \dfrac{20}{12}-\dfrac{25}{12} \right ] \right )\\
=\dfrac{5}{9}\left ( -1+1: \dfrac{-5}{12} \right )\\
=\dfrac{5}{9}\left ( -1- \dfrac{12}{5} \right )\\
=\dfrac{5}{9}\left ( \dfrac{-5}{5}- \dfrac{12}{5} \right )\\
=\dfrac{5}{9}.\dfrac{-17}{5}\\
=\dfrac{-17}{9}\\
c)\dfrac{-7}{25}.\dfrac{11}{13}+\dfrac{-7}{25}.\dfrac{2}{13}-\dfrac{18}{25}\\
=\dfrac{-7}{25}.\left [\dfrac{11}{13}+\dfrac{2}{13}  \right ]-\dfrac{18}{25}\\
=\dfrac{-7}{25}.\dfrac{13}{13}-\dfrac{18}{25}\\
=\dfrac{-7}{25}-\dfrac{18}{25}\\
=\dfrac{-7-18}{25}=\dfrac{-25}{25}=-1\\
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{7.4}{15.4}\\
\Leftrightarrow x=\dfrac{-63+28}{60}=\dfrac{-35}{60}=\dfrac{-7}{12}\\
b)\left ( 3\dfrac{1}{2}-x \right ).1\dfrac{1}{4}=-1\dfrac{1}{20}\\
\Leftrightarrow \left ( \dfrac{7}{2}-x \right ).\dfrac{5}{4}=-\dfrac{21}{20}\\
\Leftrightarrow \dfrac{7}{2}.\dfrac{5}{4}-\dfrac{5}{4}x=\dfrac{-21}{20}\\
\Leftrightarrow \dfrac{-5}{4}x=\dfrac{-21}{20}-\dfrac{35}{8}\\
\Leftrightarrow \dfrac{-5}{4}x=\dfrac{2.(-21)}{40}-\dfrac{35.5}{40}\\
\Leftrightarrow \dfrac{-5}{4}x=\dfrac{-217}{40}\\
\Leftrightarrow x=\dfrac{-217}{40}.\dfrac{-4}{5}=\dfrac{217}{50}\\
c) \left ( x+\dfrac{2}{5} \right )^2-\dfrac{2}{5}=\dfrac{6}{25}\\
\Leftrightarrow \left ( x+\dfrac{2}{5} \right )^2=\dfrac{6}{25}+\dfrac{2}{5}\\
\Leftrightarrow \left ( x+\dfrac{2}{5} \right )^2=\dfrac{6}{25}+\dfrac{10}{25}\\
\Leftrightarrow \left ( x+\dfrac{2}{5} \right )^2=\dfrac{16}{25}=\left ( \dfrac{4}{5} \right )^2\\
\Leftrightarrow x+\dfrac{2}{5}=\dfrac{4}{5}\\
\Leftrightarrow x=\dfrac{4}{5}-\dfrac{2}{5}=\dfrac{2}{5}$