Gải phuong trình `c) ( x + 1 )^2 + 2( x + 1 ) + 1 = 0 ` `d) ( x - 1 ) ( x^2 - 9 ) + x + 3 = 0 `

c) (x + 1)$^{2}$ + 2(x + 1) + 1 = 0

<=> $x^{2}$ + 2x + 1 + 2x + 1 + 1 = 0

<=> $x^{2}$ + 4x + 3 = 0

<=> $x^{2}$ + x + 3x + 3 = 0

<=> x(x + 1) + 3(x + 1) = 0

<=> (x + 1)(x + 3) = 0

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

<=> \(\left[ \begin{array}{l}x=-1\\x=-3\end{array} \right.\)

    Vậy S= {-1, -3} 

d) (x - 1)($x^{2}$ - 9) + x + 3 = 0

<=> (x - 1)(x + 3)(x - 3)+ (x + 3) = 0

<=> (x + 3)[(x - 1)(x - 3) + 1] = 0

<=> (x + 3)($x^{2}$ - 3x - x + 3 + 1) = 0

<=> (x + 3)($x^{2}$ - 4x + 4) = 0

<=> (x + 3)(x - 2)$^{2}$ = 0

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

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

<=> \(\left[ \begin{array}{l}x=-3\\x=2\end{array} \right.\) 

      Vậy S={-3, 2}