Ta có
\(\left\{{}\begin{matrix}6-6=0\\9-9=0\end{matrix}\right.\Rightarrow6-6=9-9}\\ \Rightarrow\left(3+3\right)+\left(3-3\right)=3x3-3x3\\ \Rightarrow\left(3-3\right)+\left(3-3\right)=3x3-3x3\\ \Rightarrow\left(3-3\right)\left(1+1\right)=3\left(3-3\right)\\ \Rightarrow1+1=3\)