(a-2)(a-1) - a(a+1) = a^2 - 2a -a  +2 - a^2 + a = 2(1-a)

(b-5)(b+10) + (b+6)(b-8) = b^2+10b - 5b - 50 + b^2 - 8b +6b -48 = 2b^2 - 7b - 98

(2c+3)(3c+2) - (2c+7) (2c-7) = 6c^2 + 4c + 9c^2 +6 - 4c^2 - 49 = 11c^2 + 4c - 43

(3d+5)(5d-1) - (6d-3)(2-8d) = 15d^2 - 3d + 25d - 5 -12d +48d^2 +6 - 24d = 63d^2 - 14D +1