1. Define the polynomial: f(x) = x^3 - 13x + 12
2. Use the Factor Theorem: if (x + 4) is a factor, then (f(-4)) should be 0.
3. Compute (f(-4)):
f(-4) = (-4)^3 - 13(-4) + 12
f(-4) = -64 + 52 + 12
f(-4) = -64 + 64 = 0
4. Since (f(-4) = 0), (x + 4) is a factor of (x^3 - 13x + 12).
Answer: (x + 4) is a factor.