We know that for all angles #tanA=sinA/cosA# i.e. #sinA=cosAtanA#
and #cosA=sinA/tanA#.
Hence, if #sinA# and #cosA# are negative, #tanA# is positive.
if #cosA# and #tanA# are negatve, #sinA# is positive.
and if #sinA# and #tanA# are negative, #cosA# is positive.
Hence we cannot have #sin(u/2)#, #cos(u/2)# and #tan(u/2)# all negative.
However, if #sin(u/2)# is negative, #u/2# lies in #Q3# and #Q4# i.e. #pi < u/2 < 2pi# i.e. #2pi < u < 4pi#,
if #cos(u/2)# is negative, #u/2# lies in #Q2# and #Q3# i.e. #pi/2 < u/2 < (3pi)/2# i.e. #pi < u < 3pi#
and if #tan(u/2)# is negative, #u/2# lies in #Q2# and #Q4# i.e. #pi/2 < u/2 < pi# or #(3pi)/2) < u < 2pi# i.e. either #pi < u <2pi# or #3pi < u < 4pi#
