\(x^2+4x+3=0\)

\(\Rightarrow x^2+x+3x+3=0\)

\(\Rightarrow x\left(x+1\right)+3\left(x+1\right)=0\)

\(\Rightarrow\left(x+1\right)\left(x+3\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x+1=0\Rightarrow x=-1\\x+3=0\Rightarrow x=-3\end{cases}}\)

vậy.....

k mk nha ^-^