(a^3-a^2-2a)(12-a-a^2)/(a^2-2a-3)(a^4-8a^2+2a^3)
=-a(a^2-a-2)(a^2+a-12)/(a^2-2a-3)(a^4+2a^3-8a^2)
=-a(a-2)(a+1)(a+4)(a-3)/(a-3)(a+1)(a^4+2a^3-8a^2)
=-a(a-2)(a+4)/(a^4+2a^3-8a^2)
=-a(a-2)(a+4)/[a^2(a^2+2a-8)]
=-a(a-2)(a+4)/[a^2(a+4)(a-2)]
=-1/a
(a^3-a^2-2a)(12-a-a^2)/(a^2-2a-3)(a^4-8a^2+2a^3)
=-a(a^2-a-2)(a^2+a-12)/(a^2-2a-3)(a^4+2a^3-8a^2)
=-a(a-2)(a+1)(a+4)(a-3)/(a-3)(a+1)(a^4+2a^3-8a^2)
=-a(a-2)(a+4)/(a^4+2a^3-8a^2)
=-a(a-2)(a+4)/[a^2(a^2+2a-8)]
=-a(a-2)(a+4)/[a^2(a+4)(a-2)]
=-1/a