IMO Shortlist 1967 problem 4
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arhiva2. travnja 2012. Find values of the parameter
![u](/media/m/8/a/3/8a31c0578d8711cccb064f92f92e19ca.png)
for which the expression
does not depend on
%V0
Find values of the parameter $u$ for which the expression
$$y = \frac{ \tan(x-u) + \tan(x) + \tan(x+u)}{ \tan(x-u)\tan(x)\tan(x+u)}$$
does not depend on $x.$
Izvor: Međunarodna matematička olimpijada, shortlist 1967