Evaluate giving exact values and identities. Calculator based solutions are not acceptable. Thanks for any help

Question

cos (-5pi/12)

Answer 1

5pi/12 radians = 75º

so cos(-5pi/12) = cos(-75º = cos 75º
= cos(45+30)º
= cos45cos30 - sin45sin30
= √2/2*√3/2 - √/2*1/2
= (√6 - √2)/4