Trigonometri Kelas XI

cos (a+b) = cos a cos b - sin a sin b
cos 30 = 3/4 - sin a sin b
3/4 - 1/2 akar 3 = sin a sin b

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

jawab
 
cos(α+β) + cos (α - β) = 2 cos α cos β
cos (α - β ) = 2 (cos α cos β) - cos (α + β)
cos (α - β) = 2 (3/4) - cos π/6
cos (α - β) = 3/2 - 1/2 √3 = 1/2 (3 - √3)