tan15*tan25*tan35*tan45*tan55tan65*tan75
=tan15*tan25*tan35*tan45*ctan35ctan25*ctan15
=tan15ctg15*tg25ctg25*tg35ctg35*tg45
=1
tan15*tan25*tan35*tan45*tan55tan65*tan75
=tan15*tan25*tan35*tan45*ctan35ctan25*ctan15
=tan15ctg15*tg25ctg25*tg35ctg35*tg45
=1