Question

How do you evaluate `cos^2(pi/8) - sin^2(pi/8)`?

Answer 1

`sqrt2/2`

Explanation:

Apply the trig identity: `cos 2a = cos^2 a - sin^2 a`
`cos^2 (pi/8) - sin^2 (pi/8) = cos (pi/4)`
Trig table --> `cos (pi/4) = sqrt2/2`