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Using the fact that sin (A + B) = sin A cos B + cos A sin B and the differentiation, obtain the sum formula for cosines. |
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Answer» sin (A + B) = sin A cos B + cos A sin B Diff : w:r.to B cos(A + B) x \(\frac{dA}{dB}\)= (sinA x (- sinB) + cosA x cosB) x \(\frac{dA}{dB}\) cos(A +b) = cosA cosB – sinA sinB Hence cosine formulae |
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