We want positive ratio. Try $ y = \frac{-7 + \sqrt7}9 \approx \frac-7 + 2.64589 = \frac-4.35429 \approx -0.484 $, negative. Other root: $ \frac-7 - 2.64589 < 0 $. Both negative — meaning $ A/d < 0 $, so first and last have opposite signs — impossible for $ A^2 + (A+3d)^2 = (sum)^2 $ unless not ordered. - Get link 4share