(a-1)(a+2)+(a+1)(a-2) = a^2 + 2a - a - 2 + a^2 - 2a + a - 2= a^2 + 2a - a - 2 + a^2 - 2a + a - 2= a^2 + 2a - a - a^2 + a - 4= 2a - 3
(x-1)(x-2)+(x-3)(x-4) = x^2 - 2x - x + 2 + x^2 - 4x - 3x + 12= x^2 - 3x + 2 + x^2 - 7x + 12= 2x^2 - 10x + 14
(a-1)(a+2)+(a+1)(a-2) = a^2 + 2a - a - 2 + a^2 - 2a + a - 2
= a^2 + 2a - a - 2 + a^2 - 2a + a - 2
= a^2 + 2a - a - a^2 + a - 4
= 2a - 3
(x-1)(x-2)+(x-3)(x-4) = x^2 - 2x - x + 2 + x^2 - 4x - 3x + 12
= x^2 - 3x + 2 + x^2 - 7x + 12
= 2x^2 - 10x + 14