If you would like to calculate (7 * b - 12) / (2 * a * c) when a = -2, b = 4, c = 7, you can do this using the following steps:
(7 * b - 12) / (2 * a * c) = (7 * 4 - 12) / (2 * (-2) * 7) = (28 - 12) / (- 28) = 16 / (-28) = - 4/7
a = -2, b = 4, c = 7
The correct result would be - 4/7.
