I'd do it this way:

\starttext
\startitemize[n][style=\bf]
\item\vtop{%
  \startitemize[a,horizontal,four][stopper=\)]
    \startitem
      $6(x - \dfrac{5}{12})^2 - \dfrac{1}{24}$
    \stopitem
    \startitem
      $-3(x - \dfrac{1}{3})^2 + \dfrac{1}{3}$
    \stopitem
    \startitem
      $7(x + \dfrac{5}{14})^2 + \dfrac{199}{28}$
    \stopitem
    \startitem
      $-\dfrac{1}{2}(x + 2)^2 + \dfrac{9}{2}$
    \stopitem
  \stopitemize
}
\stopitemize

\stoptext

Alexandre Christe <aleks.christe@gmail.com> 於 2023年8月22日 週二 上午2:58寫道：

> Dear ConTeXt users,
>
> Time goes by but I haven't yet found a nice solution to this issue. When
> having mathematics, I'd not like to adjust by hand the factor of \linewidth
> for the \godown command.
>
> Here's a MWE
>
> \starttext
>
> \startitemize[n][style=\bf]
>   \item \godown[-\lineheight] \startitemize
> [a,columns,four,packed,broad][stopper=),before={\blank[nowhite]}]
>     \item $6(x - \dfrac{5}{12})^2 - \dfrac{1}{24}$
>     \item $-3(x - \dfrac{1}{3})^2 + \dfrac{1}{3}$
>     \item $7(x + \dfrac{5}{14})^2 + \dfrac{199}{28}$
>     \item $-\dfrac{1}{2}(x + 2)^2 + \dfrac{9}{2}$
>   \stopitemize
> \stopitemize
>
> \stoptext
>
> Thanks in advance.
>
> Le ven. 2 sept. 2022 à 11:24, fv leung via ntg-context <ntg-context@ntg.nl>
> a écrit :
>
>>
>> \starttext
>>
>> \startitemize[n]
>> \item\godown[-\lineheight]
>>
>> \startitemize[a,columns,packed][before={\blank[nowhite]},right=\),stopper=]
>>   \item bla
>>   \item bla
>>   \item bla
>>   \item bla
>>   \stopitemize
>> \item\godown[-\lineheight]
>>
>> \startitemize[a,columns,packed][before={\blank[nowhite]},n=3,right=\),stopper=]
>>   \item bla
>>   \item bla
>>   \item bla
>>   \item bla
>>   \item bla
>>   \item bla
>>   \stopitemize
>> \item\godown[-\lineheight]
>>
>> \startitemize[a,columns,packed][before={\blank[nowhite]},n=4,right=\),stopper=]
>>   \item bla
>>   \item bla
>>   \item bla
>>   \item bla
>>   \item bla
>>   \item bla
>>   \item bla
>>   \item bla
>>   \stopitemize
>> \stopitemize
>>
>> \stoptext
>>
>> Alexandre Christe via ntg-context <ntg-context@ntg.nl> 於 2022年9月2日 週五
>> 下午5:08寫道：
>>
>>> Dear all,
>>>
>>> I'm struggling to setup a nested itemize with no blank line and several
>>> columns.
>>>
>>> What I mean is something like
>>> 1. a) bla   c) bla
>>>     b) bla   d) bla
>>>
>>> The following MWE is my starting point
>>>
>>> \starttext
>>> \startitemize[n]
>>> \item \blank[-line]
>>> \startitemize[a,horizontal,two] [margin=2cm]
>>> \item First
>>> \item Second
>>> \item Third
>>> \item Fourth
>>> \stopitemize
>>> \item \blank[-line]
>>> \startitemize[a,horizontal,columns,two]
>>> \item First
>>> \item Second
>>> \item Third
>>> \item Fourth
>>> \stopitemize
>>> \stopitemize
>>> \stoptext
>>>
>>> Thanks in advance
>>>
>>> ___________________________________________________________________________________
>>> If your question is of interest to others as well, please add an entry
>>> to the Wiki!
>>>
>>> maillist : ntg-context@ntg.nl /
>>> https://www.ntg.nl/mailman/listinfo/ntg-context
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>>>
>>> ___________________________________________________________________________________
>>>
>>
>> ___________________________________________________________________________________
>> If your question is of interest to others as well, please add an entry to
>> the Wiki!
>>
>> maillist : ntg-context@ntg.nl /
>> https://www.ntg.nl/mailman/listinfo/ntg-context
>> webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
>> archive  : https://bitbucket.org/phg/context-mirror/commits/
>> wiki     : https://contextgarden.net
>>
>> ___________________________________________________________________________________
>>
>
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to
> the Wiki!
>
> maillist : ntg-context@ntg.nl /
> https://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
> archive  : https://bitbucket.org/phg/context-mirror/commits/
> wiki     : https://contextgarden.net
>
> ___________________________________________________________________________________