the main formula is lim (1- cos X) / X = 0, when X approaches 0, and
lim sinX / X =1 when X approaches 0
lim (1-cos3x/sin3x) = lim (3x/3x) (1-cos3x/sin3x)= lim [(1-cos3x) /3x].[lim
X approaches 0 X approaches 0 X approaches 0
1/(sin3x/3x)]= 0 x 1/1=0
finally lim (1-cos3x/sin3x) =0
X approaches 0