#### Answer

(a) factor
(b) $k$

#### Work Step by Step

RECALL:
(1) The factor theorem: If P(x) is divided by $x-c$ and the remainder is 0, then $x-c$ is a factor of P(x).
(2) The remainder theorem states that if P(x) is divide by $x-c$, and the remainder is $k$, then $f(c)=k$.
Thus, the missing expression/s in the given items are:
(a) factor
(b) k