(a - 3)(a + 5) - (x + 2)(x - 1) при x = - 1/2

Выражение (a - 3)(a + 5) - (x + 2)(x - 1) при x = -1/2 будет равно:

(a - 3)(a + 5) - (x + 2)(x - 1) = (a^2 + 2a - 15) - ((-1/2 + 2)(-1/2 - 1)) = a^2 + 2a - 15 - ((3/2)(-3/2)) = a^2 + 2a - 15 - (9/4) = a^2 + 2a - 15 - 2.25 = a^2 + 2a - 17.25