Find the interval on which the expansion is valid.

$($Give your answer as an interval in the form $\backslash (\backslash$left$(\{\}^\{*\},*\backslash$right$)\backslash ).$ Use the symbol $\backslash (\backslash$infty $\backslash )$ for infinity, $\backslash (\backslash$cup $\backslash )$ for combining intervals, and an appropriate type of parenthesis $"(",")","[","]"$ depending on whether the interval is open or closed. Enter $\backslash (\backslash$varnothing $\backslash )$ if the interval is empty. Express numbers in exact form. Use symbolic notation and fractions where needed.$)$