how do I solve cos2θ = cos^2θ − 1

How do I solve cos 2 theta = cos squared theta -1
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1 Answer

LHS=cos2θ
=cos(θ+θ)
Using the identity of cos(A+B),we have
=cosθcosθ-sinθsinθ
=cos²θ-sin²θ
putting sin²θ=1-cos²θ we have,
=cos²θ-(1-cos²θ)
=cos²θ-1+cos²θ
=2cos²θ-1=RHS

by Level 1 User (660 points)

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