#cot 3x =1#
#3x=cot^-1 1#
#3x=tan^-1 (1/1)#
#3x=tan^-1 1#
#3x=pi/4 + pi n#
#x=(pi/4 + pi n)/3#
#x=pi/12 + pi/3 n#, where n are integers
#n=0, x=pi/12#
#n=1, x = (5pi)/12#
#n=2, x = (3pi)/4#
#n=3, x = (13 pi)/12#
#n=4, x = (17 pi)/12#
#n=5,x= (7pi)/4#
#S={pi/12,(5pi)/12,(3pi)/4, (13 pi)/12,(17 pi)/12, (7pi)/4}#