Lời giải:
Để các biểu thức đã cho có nghĩa thì:
a) \(x^2-8x+18\geq 0\)
\(\Leftrightarrow x^2-8x+16+2\geq 0\)
\(\Leftrightarrow (x-4)^2+2\geq 0\Leftrightarrow x\in\mathbb{R}\)
b)
\(\left\{\begin{matrix} 3x-2\geq 0\\ 3-2x\geq 0\end{matrix}\right.\Leftrightarrow \left\{\begin{matrix} x\geq \frac{2}{3}\\ x\leq \frac{3}{2}\end{matrix}\right.\Leftrightarrow \frac{2}{3}\leq x\leq \frac{3}{2}\)
c)
\(\left\{\begin{matrix} x-2\neq 0\\ \frac{3x+4}{x-2}\geq 0\end{matrix}\right.\Leftrightarrow \left[\begin{matrix} 3x+4\geq 0; x-2>0\\ 3x+4\leq 0; x-2< 0\end{matrix}\right.\)
\(\Leftrightarrow \left[\begin{matrix} x>2\\ x\leq \frac{-4}{3}\end{matrix}\right.\)
