10: ĐKXĐ: \(x\in R\)
\(\sqrt{9\left(1-x\right)^2}=15\)
=>\(3\cdot\left|x-1\right|=15\)
=>|x-1|=15:3=5
=>\(\left[{}\begin{matrix}x-1=5\\x-1=-5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=6\\x=-4\end{matrix}\right.\)
11:
ĐKXĐ: \(x\in R\)
\(\sqrt{4x^2-12x+9}=8\)
=>\(\sqrt{\left(2x\right)^2-2\cdot2x\cdot3+3^2}=8\)
=>\(\sqrt{\left(2x-3\right)^2}=8\)
=>|2x-3|=8
=>\(\left[{}\begin{matrix}2x-3=8\\2x-3=-8\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x=11\\2x=-5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{11}{2}\\x=-\dfrac{5}{2}\end{matrix}\right.\)
12: ĐKXĐ: \(x\in R\)
\(\sqrt{16-72x+81x^2}-2=0\)
=>\(\sqrt{\left(9x\right)^2-2\cdot9x\cdot4+4^2}=2\)
=>\(\sqrt{\left(9x-4\right)^2}=2\)
=>|9x-4|=2
=>\(\left[{}\begin{matrix}9x-4=2\\9x-4=-2\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}9x=6\\9x=2\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{2}{3}\\x=\dfrac{2}{9}\end{matrix}\right.\)
