Answer: (2α) = cos²(α) - sin²(α)
Step-by-step explanation:
The expression for cosine of the sum of two angles is:
cos (α + β) = cos(α)*cos(β) - sin(α)*sin(β)
in case α = β
cos ( α + α ) = cos (2α) = cos(α)*cos(α) - sin(α)*cos(α)
Hence cos (2α) = cos²(α) - sin²(α)
