Here's the way to figure this.....
Let S = 9 / [ 1 + r]
Since l r l < 1 , then 1 + l r l < 2
Look at the graph of these , here :
https://www.desmos.com/calculator/b5eiddmoz7
Substituting "x" for "r", "S" reaches a positive integer minimum of 5 inside the shaded area when x = .8 = r
Thus
S = 9 / [ 1 + .8 ] = 5
And....re-writing this in a slightly different manner, we have that
S = 9 / [ 1 - r ]
S = 9 / [ 1 - (- .8)] = 9 / [ 1 - (-4/5) ]
So..... r = -4 / 5
