Question

If $$(x + 5)$$ is a factor of $$f(x) = x^3 - 20x + 5k$$, then $$k = ?$$

Options

• –2

• –3

• 5

• –5

Answer 1

5 

Explanation:

By the Factor Theorem, $$f(-5) = -125 + 100 + 5k = 0$$, giving $$k = 5$$.