Double angle formulas: using cosine double-angle identity
3:28
Khan AcademySal Khan
Double angle formulas: using cosine double-angle identity
The cosine double angle formula tells us that cos(2θ) is always equal to cos²θ-sin²θ. For example, cos(60) is equal to cos²(30)-sin²(30). We can use this identity to rewrite expressions or solve problems. See some examples in this video.
Aug 7, 2013
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