Math CentralQuandaries & Queries


Question from Carter, a student:

let cos B = a, find cos 2B and sin 2B in terms of a and hence confirm that
cos^2 (2B) + sin^2 (2B) = 1

Hi Carter,

Use the expressions for sin(A + B) and cos (A + B) that are in my response to Matt's question. Substitute A = B. Substitute the values you obtain into cos2(2B) + sin2(2B) and simplify.


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