Question

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

Answer 1

put x=-1, and the rest will be easy

Answer 2

If x + 1 divides f(x), this means x = -1 is a root of f(x), i.e. f(-1) = 0. Plugging in x = -1 gives

f(-1) = 2 (-1)³ + k (-1) - 1 = -3 - k = 0

Solve for k; you end up with k = -3.