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chrisdbest

  • one year ago

Rewrite with only sin x and cos x. cos 3x (A) cos x - 4 cos x sin2x (B)-sin3x + 2 sin x cos x (C)-sin2x + 2 sin x cos x (D)2 sin2x cos x - 2 sin x cos x

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  1. welshfella
    • one year ago
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    Hint cos 3x = cos(2x + x)

  2. chrisdbest
    • one year ago
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    Ye s I know that.

  3. chrisdbest
    • one year ago
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    I have a headache from a slip and fall accident and just don't feel like working. I will medal you if you have the correct answer.

  4. welshfella
    • one year ago
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    but I dont think we can use that anyway because cos ( a + b) = cosa cosb - sina sinb

  5. chrisdbest
    • one year ago
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    -_-

  6. chrisdbest
    • one year ago
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    So can someone please tell me the answer

  7. welshfella
    • one year ago
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    Its not C because that simplifies to -sin 2x + sin2x = 0

  8. chrisdbest
    • one year ago
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    ohkay

  9. chrisdbest
    • one year ago
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    I know it's not D because I chose that and it was wrong

  10. welshfella
    • one year ago
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    I cant convert cos 3x into any of the options . I think there might be an error in the question. I'll plug in x = 20 degrees and see if any of them work out to 0.5 (because cos 60 = 0.5)

  11. chrisdbest
    • one year ago
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    try B then

  12. welshfella
    • one year ago
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    - sin 60 + 2 cos 20 sin 20 = -0.2232 not that one

  13. welshfella
    • one year ago
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    nor A - none of them equal cos 3x

  14. welshfella
    • one year ago
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    thers a problem with the question

  15. chrisdbest
    • one year ago
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    That's the beauty of Virtual School

  16. LynFran
    • one year ago
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    Try https://www.symbolab.com/solver/trigonometric-identity-calculator

  17. chrisdbest
    • one year ago
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    I know it's not D or B, because I just got it wrong and can't do it over again. I have been told it's not A or C by an elite, and I KEEP GETTING THE QUESTION WRONG!!!!

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