Avenged7x
Prove: sin θ  sin θ•cos2 θ = sin3 θ. You must show all work.



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Avenged7x
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idk even where to begin

myininaya
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Just thought
Maybe you can take the right hand side and show the left hand side
Try to play with this thought:
sin(3x) is sin(2x+x)

myininaya
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That should be a hint to use the sum identity for sin

Idealist10
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Memorize the identities for cos 2*theta

myininaya
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Though I could be wrong but I don't think this is an identity.

myininaya
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One way to find out is to find a counterexample

myininaya
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try theta=pi/2
does not work

Idealist10
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sin(2x)=2*sin(x)*cos(x)

Idealist10
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cos(2x)=2cos^2 (x)1

myininaya
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Maybe the problem has been written incorrectly.

myininaya
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Unless the instructions say to:
Prove if true and give a counterexample if false.
If so then I have accidentally given you the answer.

Idealist10
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cos(2x)=12sin^2 (x)
so what's sin(x)*cos(2x)?