a) \(2x-\left[x-\left(\dfrac{-3}{4}-4\right)\right]=\dfrac{13}{16}\)
\(2x-\left[x-\left(\dfrac{-19}{4}\right)\right]=\dfrac{13}{16}\)
\(2x-x-\dfrac{19}{4}=\dfrac{13}{16}\)
\(x-\dfrac{19}{4}=\dfrac{13}{16}\)
\(x=\dfrac{13}{16}+\dfrac{19}{4}\)
\(x=\dfrac{89}{16}\)
Vậy ....
b) \(\left|x-7\right|=x-7\)
\(\Leftrightarrow\left[{}\begin{matrix}x-7=x-7\\x-7=-x-7\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x-x=7+7\left(loại\right)\\x+x=7+7\left(tm\right)\end{matrix}\right.\)
\(\Leftrightarrow2x=14\)
\(\Leftrightarrow x=7\left(tm\right)\)
Vậy ................
c) \(\left|x-9\right|=9-x\)
\(\Leftrightarrow\left[{}\begin{matrix}x-9=9-x\\x-9=-9-x\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x+x=9+9\\x+x=-9+9\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}2x=18\\2x=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=9\\x=0\end{matrix}\right.\)
Vậy ...
