Maths A level - Trignometry

- sounds silly but how do I find cos(75) without using a calculator

id use the cos (x+a) = cos(x) cos(a) - sin(x) sin (a) identity and use 45 and 30 since those are exact values.
so subbing to form: cos (45+30) = cos(45) cos(30) - sin(45) sin(30)
cos(75) = (root2)/2 x (root3)/2 - (root2)/2 x 1/2 and solve from there to get (root6 - root2)/4
(that should be right 🙂 ) hope it helps!