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Rewrite with only sin x and cos x.


sin (3x) - cos (x)


Please guide me with showing work because the process of substituting is what I'm having difficulties with.

Verified Answer :

HomertheGenius

sin (3 x) - cos (x)=
= sin (2x + x) - cos (x)=
= sin 2x cos x + cos 2 x sin x - cos x = ( using additional formulas )
= 2 sin x cos² x + ( cos² x - sin² x ) sin x - cos x = 
= 2 sin x cos² x + ( 1 - sin² x - sin² x ) sin x - cos x = 
= 2 sin x cos² x + ( 1 - 2 sin² x ) sin x - cos x =
= 2 sin x cos² x + sin x  - 2 sin³ x - cos x
Answer: B )

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