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Find the interval of convergence for the power series:

$$\sum _{ n=0 }^{ \infty }{ { \left( \cfrac { x }{ 3 } \right) }^{ n } } $$

$ \left(-\cfrac{1}{3}, \cfrac{1}{3}\right)$

$\left[-\cfrac{1}{3},\cfrac{1}{3}\right]$

$ [-3, 3]$

$ (-3, 3)$