How do you verify the identity $cos(α - β) - cos(α + β) = 2 sin α sin β$ ?

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Answer 1 · 2015-04-23T17:37:04

Write out the formulas for $cos(α - β)$ and $cos(α + β)$ .
Put a minus sign between them and simplify.

How do you verify the identity cos(α - β) - cos(α + β) = 2 sin α sin βcos(α - β) - cos(α + β) = 2 sin α sin β?