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Proved that formula cos^2a - sin^2b = cos(a+b)

Answer»

ong>Answer:

Step-by-step EXPLANATION:

cos(a+b)cos(a-b) = (COSACOSB-sinasinb)(cosacosb+sinasinb)

=(cosacosb)^2-(sinasinb)^2

=cos^2a cos^2b - sin^2a sin^2b

=cos^2a (1-sin^2b) - (1-cos^a) sin^2b

=cos ^2a -sin^2b



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