\(x^2 + y^2 +2x +1 = 0\)
\(<=> (x+1)^2 + y^2 = 0\)
\(mà (x+1)^2 \)\(\ge\) 0
\(y^2 \) \(\ge\) \(0\)
\(<=>\) \(\begin{cases} (x + 1)^2 = 0\\ y^2 = 0 \end{cases}\)
\(<=>\) \(\begin{cases} x = -1 \\ y= 0 \end{cases}\)
\(Vậy (x;y) = ( -1;0)\)
Ta có: \(x^2+y^2+2x+1=0\)
\(\Rightarrow\) \(\left(x+1\right)^2+y^2=0\)
\(\Rightarrow\) \(\left[\begin{matrix}\left(x+1\right)^2=0\\y^2=0\end{matrix}\right.\)
\(\Rightarrow\) \(\left[\begin{matrix}x=-1\\y=0\end{matrix}\right.\)
Vậy: Phương trình \(x^2+y^2+2x+1=0\) có nghiệm\(\left(x;y\right)=\left(-1;0\right)\)