Упростим.
(c - 4) * (c - 2) - c * (c - 6) = c^2 - 2 * c - 4 * c + 8 - c^2 + 6 * c = -6 * c + 8 + 6 * c = 8.
Упростим.
(c - 4) * (c - 2) - c * (c - 6) = c^2 - 2 * c - 4 * c + 8 - c^2 + 6 * c = -6 * c + 8 + 6 * c = 8.