trig question

For this, we can use half angle formulas. Since 45 degrees is a common angle on the unit circle, we can easily see that it's sine and cosine is \(\frac{\sqrt 2}{2}\). Using the half angle formula for cosines, which is: \(\cos \frac{A}{2}=\pm \sqrt{\frac{1+\cos A}{2}}\), we can get our answer. 

Here is what you should do:

Plug in \(\frac{\sqrt 2}{2}\) for cos A and solve.

Good luck!