Upgrade to access all content for this subject

Find the exact $\cos{\cfrac{5\pi}{8}}$ by using the half angle formula for cosine.

$$\cfrac{\sqrt{2-\sqrt{2}}}{2}$$

$$-\cfrac{\sqrt{2-\sqrt{2}}}{2}$$

$$-\cfrac{\sqrt{2+\sqrt{2}}}{2}$$

$$\cfrac{\sqrt{2+\sqrt{2}}}{2}$$

$$\cfrac{\sqrt{2}}{2}-1$$