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anonymous
 one year ago
Rewrite with only sin x and cos x. cos 3x
Please help me understand this. It is so confusing to me
anonymous
 one year ago
Rewrite with only sin x and cos x. cos 3x Please help me understand this. It is so confusing to me

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anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Use the property of compound angles, in which \[\cos3\theta=\cos(2\theta+\theta)\] You should also know that the expansion of\[\cos2\theta=12\sin ^{2}\theta =2\cos ^{2}\theta1\] Also in compound angles, use the property that:\[\cos(A+B)=cosAcosBsinAsinB\] Also take note that \[\sin2\theta=2\sin \theta \cos \theta \] Moving onto the exercise, we get\[\cos3x=\cos(2x+x)=\cos2xcosx  \sin2xsinx= (2\cos ^{2}x1)cosx  (2sinxcosx)sinx\]

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Further expanding, we get\[2\cos ^{3}xcosx  2\sin ^{2}xcosx\]

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0that all makes sense but that matches none of the answers
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