a) Ta có: \(\left(-12\right)-\left|13-x\right|=-21\)
\(\Leftrightarrow-\left|x-13\right|-12=-21\)
\(\Leftrightarrow-\left|x-13\right|=-9\)
\(\Leftrightarrow\left|x-13\right|=9\)
\(\Leftrightarrow\left[{}\begin{matrix}x-13=9\\x-13=-9\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=22\\x=4\end{matrix}\right.\)
Vậy: \(x\in\left\{22;4\right\}\)
b) Ta có: \(8\le\left|x\right|< 9\)
\(\Leftrightarrow\left|x\right|=8\)
\(\Leftrightarrow x\in\left\{8;-8\right\}\)
Vậy: \(x\in\left\{8;-8\right\}\)
c) Ta có: \(x-\left(-25+x\right)=13-x\)
\(\Leftrightarrow x+25-x-13+x=0\)
\(\Leftrightarrow x+12=0\)
hay x=-12
Vậy: x=-12
d) Ta có: \(\left(15-30\right)+x=x-\left(27-\left|-8\right|\right)\)
\(\Leftrightarrow x-15=x-\left(27-8\right)\)
\(\Leftrightarrow x-15-x+19=0\)
\(\Leftrightarrow-4=0\)(vô lý)
Vậy: \(x\in\varnothing\)
