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**Subject**: **Re: Fun math puzzle: cin(X)**
**From**: Tim Hill <drtimhill@...>
**Date**: Thu, 4 Apr 2019 15:52:41 -0700

> On Apr 4, 2019, at 12:03 AM, Dirk Laurie <dirk.laurie@gmail.com> wrote:
>
> Op Do. 4 Apr. 2019 om 01:14 het Albert Chan <albertmcchan@yahoo.com> geskryf:
>>
>> Comes across a fun math puzzle. :-)
>>
>> Design a function cin(X), such that cin(cin(cin(X))) = sin(X)
>>
>> cin(X) must be smooth function, and at least 10 digits accurate.
>>
>> In other words, cin(cin(cin(X))) / sin(X) = 1.00000 00000
>>
>> What is the value of cin(2.019) ?
>
> Since you post it on this list, one assumes that the calculation musr
> be done in Lua :-)
>
> Am I allowed the luxury of requiring luafft (available from LuaRocks)?
>
There is of course the “cheat” answer, which highlights how careful you need to be when setting puzzles:
do
local c = 0
function cin(x) c = c + 1; return ((c % 3) == 0) and sin(x) or x end
end
—Tim