Question

22. What is the value of k such that x - 6 is a factor of

f(x) = 3x³ - 17x² - kx + 18? Justify your answer.

Answer 1

k = 9

Explanation:

According to the Factor theorem, if (x - a) is a factor of f(x) then f(a) = 0

given (x - 6) is a factor of f(x) then f(6) = 0 , that is

3(6)³ - 17(6)² - 6k + 18 = 0

3(216) - 17(36) - 6k + 18 = 0

648 - 612 - 6k + 18 = 0

36 - 6k + 18 = 0

54 - 6k = 0 ( subtract 54 from both sides )

- 6k = - 54 ( divide both sides by - 6 )

k = 9