\(a.x^2+4x+3=x^2+x+3x+3=x\left(x+1\right)+3\left(x+1\right)=\left(x+3\right)\left(x+1\right)\)
\(b.x^2+8x+12=x^2+2x+6x+12=x\left(x+2\right)+6\left(x+2\right)=\left(x+6\right)\left(x+2\right)\)
\(c.x^2-5x+6=x^2-2x-3x+6=x\left(x-2\right)-3\left(x-2\right)=\left(x-3\right)\left(x-2\right)\)
\(d.x^2-x+6\) (Vì pt này vô nghiệm nên ko tách đc thành nhân tử)