tan−1(tan1−θ)=1−θ when
−π2<θ<π2
θ>4−π4
θ<4−π4
4−π24<θ≤1
Clearly, 1−θ is real, If θ≤1.
Now,
tan−1(tan1−θ)=1−θ
⇒ 0≤1−θ<π2 and θ≤1
⇒ 0≤1−θ<π24 and θ≤1
⇒ −1≤−θ≤π24−1 and θ≤1
⇒ 1−π24<θ≤1 and θ≤1⇒4−π24<θ≤1