The
function corresponding to the range 
,
{0}
2
−π π2
 −




is called the principal value branch
of cosec–1 We thus have principal branch as
cosec–1  : R – (–1, 1) → 
,
{0}
2
−π π2
 −




The graphs of y = cosec x and y = cosec–1 x are given in Fig 2 3 (i), (ii) Also, since sec x = 
1
cos x , the domain of y = sec x is the set R – {x : x = (2n + 1) 2
π ,
n ∈ Z} and range is the set R – (–1, 1)