Find the interval of convergence of

(x^2n)/((-3)^n)

I already found out that the boundaries of this Interval are [math]-{\sqrt{3}}[/math] and [math]{\sqrt{3}}[/math].

When I try to check the boundaries Insertertet, I get the soultion, that both have to be excluded. But one Series calculator in the Internet said, [math]-{\sqrt{3}}[/math] has to be included. That confuses me, because when I insert this boundary, i get the same series as when I insert the other boundaries.

I am very thankful for any advises!