For a positive integer n, let fn(θ)=(tanθ2)(1+secθ)(1+sec2θ)(1+sec4θ)....(1+sec2nθ). Then
convert the given equation in the form of \sin and \cos then
we have
fn(θ)=sinθ2(1+cosθ)(1+cos2θ)(1+cos4θ).....(1+cos2nθ)cosθ2cosθcos2θcos4θ.....cos2nθ
=sinθ2(2cos2θ2)(2cos2θ)(2cos22θ).....(2cos2n−1θ)cosθ2cosθcos2θcos4.....cos2nθ
=2n+1sinθ2cosθ2cosθcos2θ......cos2n−1θcos2nθ
=sin2nθcos2nθ=tan2nθ
putting values
f2(π16)=tan22(π16)=1
f3(π32)=1,f4(π64)=1,f5(π128)=1