a)x^2-6x+9-y^2 b)x^2-x-6=0 c)x^2+4x+3=0 d)x^2+4x-y^2+4 giúp mk nhanh vs ak

a) $x^2 – 6x + 9  – y^2 = (x – 3)^2 – y^2 = (x – y – 3)(x + y – 3)$

b) $x^2 – x – 6 = 0$

    $x^2 + 2x – 3x – 6 = 0$

    $x(x +2) – 3(x+2) = 0$

     $(x-3)(x+2)= 0$

$<=> \left[ \begin{array}{l}x-3 = 0\\x+ 2= 0\end{array} \right. <=> \left[ \begin{array}{l}x=3\\x=-2\end{array} \right. $

c) $x^2 + 4x + 3 = 0$

   $x^2 + x + 3x + 3 = 0$

   $(x+ 1)(x+3) = 0$

$<=> \left[ \begin{array}{l}x+3 = 0\\x+1= 0\end{array} \right. <=> \left[ \begin{array}{l}x=-3\\x=-1\end{array} \right. $

d) $x^2 + 4x  – y^2 + 4$

 $=(x + 2)^2 – y^2$

 $=(x – y + 2))(x + y + 2)$