tolong dijawab menggunakan cara trims'

jawab

a=alpa
b=beta
cos π/6 = cos 30 = 1/2 √3

cos (a+ b) = cos a cos b - sin a sin b
cos (π/6) = 3/4 - sin a sin b
1/2 √3 = 3/4 - sin a sin b
sin a sin b = 3/4 - 1/2√3  

cos (a-b)= cos a cos b + sin a sin b
cos (a-b)= 3/4 + 3/4  - 1/2 √3 = 3/2 - 1/2 √3 = 1/2 (3 - √3)