Question

Given f(x)=3x^3+2x+k and x+1 is a factor of f(x) then what is the value of k

Answer 1

k = 5

Explanation:

Given that (x + 1) is a factor of f(x) then f(- 1) = 0

f(- 1) = 3(- 1)³ + 2(- 1) + k

= 3(- 1) - 2 + k

= - 3 - 2 + k

= - 5 + k

Then - 5 + k = 0 ( add 5 to both sides )

k = 5