Question 175837
cos(5π/12) = cos(π/6 + π/4)

cos (a + b) = cos a cos b - sin a sin b
cos (π/6 + π/4) = cos π/6 cos π/4 - sin π/6 sin π/4
= √3 / 2 * √2 / 2 - 1/2 * √2 / 2
= √6 / 4 - √2 / 4
={{{highlight((sqrt(6)-sqrt(2))/4)}}}