If one root of the quadratic equation x^2 + 4x + k = 0 is twice the other root, what is the value of k?
Answer: A. -8
Let the roots be r and 2r. Then, r + 2r = -4 (sum of roots) gives 3r = -4, so r = -4/3. The product of the roots is r(2r) = k, leading to k = -8/3 * 2 = -8.