My homework is on finding maximum and minimum values and critical points in a function. Is g( )= 4 -tan differentiable everywhere?

My homework is on finding maximum and minimum values and critical points in a function. Is g(θ)=4θ-tanθ differentiable everywhere? I know the derivative of g(θ)= 4-csc^2(θ) but from there I dont know how to break this down where g'(θ)=0