\(x^2+2x+3=0\)\(\Rightarrow\left(x^2+2x+1\right)+2=0\)\(\Rightarrow\left(x+1\right)^2+2=0\)(vô lý do \(\left(x+1\right)^2+2\ge2>0\))Vậy \(S=\varnothing\)Câu trả lời: \(x^2+2x+3=0\)\(\Rightarrow\left(x^2+2x+1\right)+2=0\)\(\Rightarrow\left(x+1\right)^2+2=0\)(vô lý do \(\left(x+1\right)^2+2\ge2>0\))Vậy \(S=\varnothing\)