(√3)TanΘ = 3SinΘ
=> (√3)(SinΘ/CosΘ) = 3SinΘ [Using: TanA = SinA/CosA]
=> (SinΘ/CosΘ) / SinΘ = 3 / (√3)
=> (SinΘ/CosΘ) / SinΘ = (√3)2 / (√3)
=> 1/CosΘ = √3
=> CosΘ = 1/√3 [Taking reciprocals both sides]
=> (CosΘ)2 = (1/√3)2 [Squaring both sides]
=> Cos2Θ = 1/3
=> (-2)*Cos2Θ = (-2)*(1/3) [Multiplying (-2) both sides]
=> -2Cos2Θ = -2/3
=> 1 - 2Cos2Θ = 1 - 2/3 [Adding 1 both sides]
=> (Sin2Θ+Cos2Θ) - 2Cos2Θ = (3-2)/3
=> Sin2Θ - Cos2Θ = 1/3