Bài 1 :
\(A=\dfrac{2x+6}{\left(x+3\right)\left(x-2\right)}\\ ĐKXĐ:x\ne-3;x\ne2\)
\(A=\dfrac{2x+6}{\left(x+3\right)\left(x-2\right)}=0\\ \Leftrightarrow\dfrac{2x+6}{\left(x+3\right)\left(x-2\right)}=\dfrac{0}{\left(x+3\right)\left(x-2\right)}\\ \Leftrightarrow2x+6=0\\ \Leftrightarrow2x=-6\\ \Leftrightarrow x=-3\left(loại\right)\)
\(B=\dfrac{x^2-9}{x^2-6x+9}\\ ĐKXĐ:x\ne3;x\ne-3\)
\(B=\dfrac{x^2-9}{x^2-6x+9}=0\\ \Leftrightarrow\dfrac{x^2-3^2}{\left(x-3\right)^2}=0\\ \Leftrightarrow\left(x-3\right)\left(x+3\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x-3=0\\x+3=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=3\left(loại\right)\\x=-3\left(loại\right)\end{matrix}\right.\)
