Jawabanmu

Jawaban paling cerdas!
2014-06-07T20:33:38+07:00
α - β = π/5 , cosα . cosβ = 1/4 .
Cos (α - β) = cosαcosβ + sinαsinβ
Cos π/5     =      1/4 + SinαSinβ
1/4√(10- 2√5)  = 1/4 + SinαSinβ
SinαSinβ = 1/4√(10-2√5) - 1/4 = 1/4(√(10-2√5) - 1)
  atau langsung saja
Cos (α - β) = Cos π/5 = 1/4(√(10 - 2√5)

2 5 2