a) \(\left|x-\frac{2}{5}\right|-\frac{1}{4}=0\)
=> \(\left|x-\frac{2}{5}\right|=\frac{1}{4}\)
\(\Rightarrow\orbr{\begin{cases}x-\frac{2}{5}=\frac{1}{4}\\x-\frac{2}{5}=-\frac{1}{4}\end{cases}}\Rightarrow\orbr{\begin{cases}x=\frac{13}{20}\\x=\frac{3}{20}\end{cases}}\)
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b) \(\left|x+0,8\right|-2,9=-12\)
\(\Rightarrow\left|x+0,8\right|=-12+2,9\)
\(\left|x+0,8\right|=-9,1\)
\(\Rightarrow\orbr{\begin{cases}x+0,8=9,1\\x+0,8=-9,1\end{cases}}\Rightarrow\orbr{\begin{cases}x=8,3\\x=-9,9\end{cases}}\)
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c) |x-0,987|+6,2=-3
|x-0,987|=-3-6,2
|x-0,987|=-9,2
\(\Rightarrow\orbr{\begin{cases}x-0,987=-9,2\\x-0,987=9,2\end{cases}}\Rightarrow\orbr{\begin{cases}x=-8,213\\10,187\end{cases}}\)
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