Question

8cos³20°-6cos20°=. ans is =1

Answer 1

Cos(3Θ) = $4Cos^{3}(Θ)$ - 3Cos(Θ)
multiply '2' on both sides and replace Θ=20
2Cos(60) = $8Cos^{3}(20)$ - 6Cos(20) = 1