Question

Attached is the problem, if anyone could help me and explain this I would be grateful.

Answer 1

Let's say that, that equals some angle θ
thus    $\bf sec^{-1}(1)=\theta \iff sec(\theta)=1\\\\ -----------------------------\\\\ sec(\theta)=\cfrac{1}{cos(\theta)}\qquad thus\\\\ -----------------------------\\\\ \cfrac{1}{cos(\theta)}=1\implies \cfrac{1}{1}=cos(\theta)\implies 1=cos(\theta) \\\\\\ \textit{now, taking }cos^{-1}\textit{ to both sides} \\\\\\ cos^{-1}(1)=\theta$

so.. .check your Unit Circle, what is that angle anyway?