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Avenged7x

  • one year ago

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

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  1. Avenged7x
    • one year ago
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    idk even where to begin

  2. myininaya
    • one year ago
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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)

  3. myininaya
    • one year ago
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    That should be a hint to use the sum identity for sin

  4. Idealist10
    • one year ago
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    Memorize the identities for cos 2*theta

  5. myininaya
    • one year ago
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    Though I could be wrong but I don't think this is an identity.

  6. myininaya
    • one year ago
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    One way to find out is to find a counterexample

  7. myininaya
    • one year ago
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    try theta=pi/2 does not work

  8. Idealist10
    • one year ago
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    sin(2x)=2*sin(x)*cos(x)

  9. Idealist10
    • one year ago
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    cos(2x)=2cos^2 (x)-1

  10. myininaya
    • one year ago
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    Maybe the problem has been written incorrectly.

  11. myininaya
    • one year ago
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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.

  12. Idealist10
    • one year ago
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    cos(2x)=1-2sin^2 (x) so what's sin(x)*cos(2x)?

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