\(f\left(x\right)=x^2+2x+3\)
\(\Leftrightarrow x^2+2x+1+2\)
\(\Leftrightarrow\left(x+1\right)^2+2\)
Vì \(\left(x+1\right)^2\ge0\)=>\(\left(x+1\right)^2+2\ge2\)
Vậy PT ko có nghiệm
\(x^2+2x+3=0\)
\(\Rightarrow x^2+2x+1+2=0\)
\(\Rightarrow\left(x+1\right)^2+2=0\)( vô lý )
=> Đa thức vô nghiệm
\(f\left(x\right)=x^2+2x+3=\left(x^2+2x+1\right)+2=\left(x+1\right)^2+2\)
Vì \(\left(x+1\right)^2\ge0\Rightarrow f\left(x\right)=\left(x+1\right)^2+2\ge2>0\)
Vậy .....