Answer
$- \dfrac{\sqrt{3}}{2}$
Work Step by Step
$\cos{\dfrac{A}{2} } = - \sqrt{\dfrac{1+\cos{A}}{2}} = - \sqrt{\dfrac{1+0.5}{2}}$
$\cos{\dfrac{A}{2} } = - \dfrac{\sqrt{3}}{2}$
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.