`a.`
`x^2-6x+9-y^2`
`=>(x-3)^2-y^2`
`=>(x-y-3)(x+y-3)`
`b.`
`x^2-x-6=0`
`=>x^2+2x-3x-6=0`
`=>(x-3)(x+2)=0`
`=>\left[\begin{matrix} x-3=0\\ x+2=0\end{matrix}\right`
`=>\left[\begin{matrix} x=3\\ x=-2\end{matrix}\right`
`c.`
`x^2+4x+3=0`
`=>x^2+3x+x+3=0`
`=>(x+1)(x+3)=0`
`=>\left[\begin{matrix} x+3=0\\ x-+1=0\end{matrix}\right`
`=>\left[\begin{matrix} x=-3\\ x=-1\end{matrix}\right`
`d.`
`x^2+4x-y^2+4`
`=>(x+2)^2-y^2`
`=>(x-y+2)(x+y+2)`
( Thông cảm cho mình nhé, mình chưa hiểu latex cho lắm. )
