-2x^2+12x-18

 -2x2 + 12x - 18 = 0
Делим на 2:
-x2 + 6x - 9 = 0
D = b2 - 4ac
D = 36 - 36 = 0

x = - b/2a
x = 6/2= 3
Ответ: x = 3

ax^2+bx+c=a(x-x1)(x-x2) 

  -2x^2+12x-18=-2(x-3)(x-3)