Respuesta :
x^2 - 18x + 81 = 0
x^2 - 9x - 9x + 81 = 0
x(x - 9) - 9(x - 9) = 0
(x - 9)(x - 9) = 0
(x - 9)^2 = 0
x - 9 = 0
x = 9
x^2 - 9x - 9x + 81 = 0
x(x - 9) - 9(x - 9) = 0
(x - 9)(x - 9) = 0
(x - 9)^2 = 0
x - 9 = 0
x = 9