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Write the expression as a single trigonometric function. cos6xcos3x-sin6xsin3x

1 Answer

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cos (α+β)=cosα cosβ - sinα sinβ
In this case:
cos α=cos 6x
cos β=cos 3x
sin α=sin 6x
sin β=sin 3x

Then:
cos 6x cos 3x - sin 6x sin 3x=cos(6x + 3x)= cos 9x

Answer:
cos 6x cos3x - sin 6x sin3x= cos 9x
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User Nnamdi
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