-a^2 + a b + a c -
 b c + (4 a - 2 a^2 - 2 b - 2 c + 2 b c + a^2 k - a b k - a c k +
    b c k) x + (-3 + 2 a + 2 b - a b + 2 c - a c - b c - 2 a k + b k +
     a b k + c k + a c k - 2 b c k) x^2 + (k - b k - c k + b c k) x^3