(x+1)^2 * (a^2 - 7 x + a+13) = x^4 - 5x^3 + ax^2 + 2(a+13)x + a+13b = 2a + 19c = a + 13 a - b + c = a - 2a - 19 + a + 13 = -6 (a - b + c)^-2 = 1/36
