##390 = 360+30 = 30##
The ratios of 390 are the same as the ratios of 30.
##sin 390 = sin (30 + 360) = sin 30 = 1/2##
##cos 390 = cos (30 + 360) = cos 30 = sqrt3/2##
##tan 390 = tan 30 = 1/sqrt3 = sqrt3/3##
##cot 390 = 1/(tan 30) = sqrt3/1##
##sec 390 = 1/cos 30 = 2/sqrt3##
##csc 390 = 1/(sin 30) = 2/1##