Evaluate: sec θ √(1 - sin²θ) 

let A = sec θ √(1 - sin²θ)

Because sin²θ + cos²θ  =  1, we have  

cos²θ  =  1 - sin²θ

Then, A  =  sec θ √cos²θ

A  =  sec θ ⋅ cos θ

A  =  sec θ ⋅ ($\frac{1}{\mathrm{sec\theta }}$)

A  =  $\frac{\mathrm{sec\theta }}{\mathrm{sec\theta }}$
A  =  1