\(\frac{-3}{5}< x< \frac{1}{7}\Leftrightarrow\left\{{}\begin{matrix}x+\frac{3}{5}>0\\x-\frac{1}{7}< 0\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}\left|x+\frac{3}{5}\right|=x+\frac{3}{5}\\\left|x-\frac{1}{7}\right|=-x+\frac{1}{7}\end{matrix}\right.\)
Khi đó: \(C=x+\frac{3}{5}-x+\frac{1}{7}+\frac{4}{5}=\frac{54}{35}\)
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