sin(θ + 15°) = 3/√12 হলে cos2θ = কত?

Question: sin(θ + 15°) = 3/√12 হলে cos2θ = কত?Solution:sin(θ + 15°) = 3/√12⇒ sin(θ + 15°) = 3/(2√3)⇒ sin(θ + 15°) = √3/2⇒ sin(θ + 15°) = sin60°⇒ θ + 15° = 60°⇒ θ = 45°Now,cos2θ = (cos 45°)2= (1/√2)2= 1/2