\(x+3=\left(x+3\right)^2\)
\(\Leftrightarrow\left(x+3\right)-\left(x+3\right)^2=0\)
\(\Leftrightarrow\left(x+3\right)\left(1-x-3\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(-x-2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+3=0\\-x-2=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=-2\end{matrix}\right.\)
`x+3=(x+3)^2`
`<=>x+3=x^2+6x+9`
`<=>x^2+6x+9-x-3=0`
`<=>x^2+5x+6=0`
`<=>x^2+2x+3x+6=0`
`<=>x(x+2)+3(x+2)=0`
`<=>(x+3)(x+2)=0`
`<=>` \(\left[ \begin{array}{l}x+3=0\\x+2=0 \end{array} \right.\) `<=>` \(\left[ \begin{array}{l}x=-3\\x=-2\end{array} \right.\)
Vậy pt đã cho có tập nghiệm là : `S={-3;-2}`
Ta có: \(\left(x+3\right)^2=x+3\)
\(\Leftrightarrow\left(x+3\right)^2-\left(x+3\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(x+2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=-2\end{matrix}\right.\)
