Obscure polynomial

Since $f(2) = 0$ , we have that $f(2) = 16 - 24a+ 4b - 4b + 8 = 0 \leftrightarrow a = 1$ .

By Vieta's Formulae, the sum of the roots of the polynomial is $3$ . Since one of them is $2$ , the sum of its other roots is $\boxed{1.}$

---

This can also be done by Briot-Ruffini's Algorithm and Girard's Relations.

Since f(2) = 0, we have a = 1, Now, Sum of roots = 3a/1 = 3. One root is 2, therefore sum of others is 1.