a: ĐKXĐ: \(x\in R\)
\(\sqrt{\left(x+3\right)^2}=12\)
=>\(\left|x+3\right|=12\)
=>\(\left[{}\begin{matrix}x+3=12\\x+3=-12\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=9\\x=-15\end{matrix}\right.\)
b: ĐKXĐ: x>=1
\(\sqrt{25x-25}-\sqrt{9x-9}=10\)
=>\(5\sqrt{x-1}-3\sqrt{x-1}=10\)
=>\(2\sqrt{x-1}=10\)
=>x-1=25
=>x=26(nhận)