Respuesta :

12) x² - 6x +9 = 0        9=(-3)*(-3),  -6= -3+(-3)
 (x-3)(x-3)=0
x-3=0
x=3

 x² - 6x +9 = 0  ---- also can be soled as perfect square,
x²-2*3x+3² = (x-3)³
(x-3)² = 0
x-3=0

13)
3= 2x² - 5x
2x² -5x -3 = 0
2x²+x - 6x-3 =0
x(2x+1) - 3(2x+1)=0
(2x +1)(x - 3) = 0
2x+1 = 0, or x-3=0
x= -1/2, x=3

14) 
3 - 12 = -9x²
- 9 = -9x²
1=x²
x² -1 = 0
(x-1)(x+1)=0
x-1=0 , x+1=0
x=1, x= - 1

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