Try braces about the “12” as in
\sqrt{12}{a^{11}}

Alan


On Mon, Sep 23, 2013 at 3:55 AM, Xan <dxpublica@telefonica.net> wrote:

> Hi,
>
> \sqrt[12]{a^{11}}
>
> produces me:
>
> \sqrt[1]{2} a^{11}
>
> What happens there?
>
> Xan.
>
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