find all critical numbers of the function f (θ) = 2secθ +tanθ when -14<θ -12

Answer 1

f'(θ) = 2secθ tanθ + sec^2θ
= (2sinθ + 1)/cos^2θ
So where is f'(θ) zero or undefined?

clearly at θ = odd multiples of π/2, since cosθ=0
where else?