Упростите  (a+1)∙(a–1)∙(a–2) –a∙(a²–2a–1)

(а²-1)(а-2)-а³+2а²+а=а³-2а²-а+2-а³+2а²=2-а

= (а^2 - a +a - 1) (a-2) - a^3 + 2a^2 + a= (a^2 - 1)(a-2) - a^3 + 2a^2+a = a^3 - 2a^2 - a + 2 - a^3 + 2a^2 + a =2