9x^2 - 7x - 4 = 0
(9x^2 - 7x) - 4 = 0
9(x^2 - (7/9)x) - 4 = 0
9(x - (7/18))^2 - 9(7/18)^2 - 4 = 0
9(x - (7/18))^2 - (49/36) - 4 = 0
9(x - (7/18))^2 = 193 / 36
(x - (7/18))^2 = 193 / 324
x - (7/18) = sqrt(193) / 18 or = -sqrt(193) / 18
x = (7 + sqrt(193)) / 18 or x = (7 - sqrt(193)) / 18