Find all r for which the infinite geometric series \(2 + 6r + 18r^2 + 54r^3 + \dotsb.\) is defined. Enter all possible values of r, as an interval.
Since we have a geometric series, the possible values of r are in the interval (-1,1).
Since each term is 3r times the preceding term, this will be a geometric series for whatever number you choose for r.
Interval form: (-infinity, infinity).