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Convert the following products into the sum or difference of sines and cosines: $$2 \cos 4 x \cos 3 x$$
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## QuestionMathsClass 11

Convert the following products into the sum or difference of sines and cosines: $$2 \cos 4 x \cos 3 x$$

As we know, $$2 \cos A \cos B=\cos (A-B)+\cos (A+B)$$
Therefore,
$$2 \cos 4 x \cos 3 x=\cos(4 x+3 x)+\cos (4x-3x)$$
$$= \cos7x+\cos x$$