The inverse of a function f:A→B exists if f is one-one onto i.e.,
y=f( x )⇒ f −1 ( y )=x .
The given inverse trigonometry function is tan −1 ( − 3 ) .
Let,
tan -1 ( − 3 )=y
tany=− 3 =−tan π 3 =tan( − π 3 )
Since, the range of the principle value branch of tan -1 is ( − π 2 , π 2 ) .
− π 3 ∈( − π 2 , π 2 )
Thus, the principle value of tan −1 ( 3 ) is ( − π 3 ) .