3) (4a^2-3a+5)/(a^3-1) - (1-2a)/(a^2+a+1) + 6/(1-a)

Factor the denominator of the first term: a^3-1 = (a-1)(a^2+a+1).

Rewrite the second term with a common denominator: -(1-2a)(a-1)/(a^3-1).

Simplify the expression to: 3/(a-1).