Select all of the following that are quadratic equations. 2 x2+ 12 x = 0, x2 - 2 x = 4, x + 1 x3 - 6 x2 + 8 = 0, 5 x - 3 = 0, 5 x - 1 = 3x + 8, 9 x2 + 6 x - 3 = 0