a, \(\left(\dfrac{5}{6}:x-1\dfrac{1}{4}\right)^4=\dfrac{81}{16}\)
\(\Leftrightarrow\left(\dfrac{5}{6}:x-1\dfrac{1}{4}\right)^4=\left(\dfrac{3}{2}\right)^4\)
\(\Leftrightarrow\left[{}\begin{matrix}\dfrac{5}{6}:x-\dfrac{5}{4}=\dfrac{3}{2}\\\dfrac{5}{6}:x-\dfrac{5}{4}=\dfrac{-3}{2}\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}\dfrac{5}{6}:x=\dfrac{11}{4}\\\dfrac{5}{6}:x=\dfrac{7}{12}\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{35}{66}\\x=\dfrac{10}{7}\end{matrix}\right.\)
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b, \(\left|\dfrac{2}{5}x-0,2\right|.1\dfrac{1}{4}-2=1,5\)
\(\Leftrightarrow\left|\dfrac{2}{5}x-0,2\right|.\dfrac{5}{4}=\dfrac{3}{5}\)
\(\Leftrightarrow\left|\dfrac{2}{5}x-0,2\right|=\dfrac{12}{25}\)
\(\Leftrightarrow\left[{}\begin{matrix}\dfrac{2}{5}x-0,2=\dfrac{12}{25}\\\dfrac{2}{5}x-0,2=\dfrac{-12}{25}\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}\dfrac{2}{5}x=\dfrac{17}{25}\\\dfrac{2}{5}x=\dfrac{-7}{25}\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{17}{10}\\x=\dfrac{-7}{10}\end{matrix}\right.\)
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