For Problems 28–30: The numbers \(a\), \(b\), and \(c\) are between 2 and 18, such that (i) their sum is 25, (ii) the numbers 2, \(a\), and \(b\) are consecutive terms of an A.P., (iii) the numbers \(b\), \(c\), 18 are consecutive terms of a G.P.Roots of the equation \(ax^2 + bx + c = 0\) are