Answer
$-\sqrt{10}$
Work Step by Step
From problem 21 $\to \cos{\dfrac{A}{2}} = -\dfrac{\sqrt{10}}{10}$
$\because \sec{\dfrac{A}{2}} = \dfrac{1}{\cos{\dfrac{A}{2}}}$
$\therefore \sec{\dfrac{A}{2}} = -\sqrt{10}$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.