Question 953244
Find the exact value by using a half-angle identity. 

cosine of five pi divided by twelve.
========================
cos(5pi/12)
---
cos(5pi/6) = -sqrt(3)/2
Use cos^2(x/2), it's simpler than cos(x/2)
cos^2(x/2) = (1 + cos(x))/2
{{{cos^2(5p/12) = (1 - sqrt(3))/2 = (2 - 2sqrt(3))/4}}}
{{{cos(5pi/12) = sqrt(2 - 2sqrt(3))/2}}}  (positive in Q2)