If the quadratic equation 3x² - 12x + k = 0 has roots that differ by 2, what is the value of k?
Answer: A. 18
Let the roots be r and r+2. The sum of the roots is 12/3 = 4, so 2r + 2 = 4, giving r = 1. The product of the roots is k/3 = r(r+2) = 1*3 = 3, thus k = 18.