Prof. Martin tried to solve the quadratic equation y = 8x2 − 5x − 3 by completing the square, but she made a mistake.

In which line of her work shown below did she make the mistake?
8x2 − 5x − 3 = 0
[Line 1] ⇒ 8x2 − 5x = 3
[Line 2] ⇒ x2 − 0.625x = 0.375
[Line 3] ⇒ x2 − 0.625x + 0.09765625 = -1.25 + 0.09765625
[Line 4] ⇒ (x − 0.3125)2 = -1.25 + 0.09765625
[Line 5] ⇒ (x − 0.3125)2 = 0.47265625
[Line 6] ⇒ x − 0.3125 = ±√(0.47265625)
[Line 7] ⇒ x = ±√(0.47265625) − 0.3125
[Line 8] ⇒ x = -0.375 or 1.000, rounded to 3 decimal places

Line 5

Line 4

Line 6

Line 7