\(1,A=9-\sqrt{x+3}\le9\)
Dấu \("="\Leftrightarrow x+3=0\Leftrightarrow x=-3\)
\(2,B=6+\sqrt{x^2+2x-3}\ge6\)
Dấu \("="\Leftrightarrow x^2+2x-3=0\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-3\end{matrix}\right.\)
\(3,C=\sqrt{x^2+2x+3}=\sqrt{\left(x+1\right)^2+2}\ge\sqrt{2}\)
Dấu \("="\Leftrightarrow x=-1\)