Question

Α - β = π/4 , cosα x cosβ = 1/5 . Maka, Cos α - β = .. ?

Answer 1

Cos α-β= cos α cosβ+sin α sin β
cos(45)=1/5+sin α sinβ
1/2 √2=1/5+sinα sin β
sinα sinβ= 1/2 √2-1/5
sehingga cos α-β= cos α cos β + sin α sin β=1/5+1/2 √2- 1/5= 1/2 √2