If sec ⁡x=−√2, and 180°<x<270°, what is cos⁡(x/2).

Question

If sec ⁡x=−√2, and 180°<x<270°, what is cos⁡(x/2) in radical form?

Answer 1

Try using the half angle formula for cos(x/2).

cos(x/2) = ± √ [(1+cos(x)/2]