Question

Help me friends!!!!!!

Answer 1

cos 60° = cos (2×30°) = 2 cos^2 (30°) - 1 = 2×3/4 - 1 = 3/2 - 1 = 1/2

Answer 2

cos 0 = 30°
given formula
cos 20 = 2 cos ^20-1 [ 0 = 30°]
cos 2(30) = 2 cos^2(30)-1
cos 60° = cos ^2 60° - 1 [ cos 60° = 1/2]
1/2 = (1/2)^2 -1
cos = root 3