At θ=90∘, which of the two angles are not defined?
cot θ,sin θ
tan θ,cosec θ
cot θ,tan θ
tan θ,sec θ
As tan θ=sin θcos θ and at θ=90∘,cos 90∘=0. So, tan θ is not defined. Similarly, sec θ=1cos θ. So, sec θ is not defined at θ=90∘.