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allison_

  • 3 years ago

Verify the identity. cos 4x + cos 2x = 2 - 2 sin^2 2x - 2 sin^2 x

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  1. Tushara
    • 3 years ago
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    cos(4x)=cos(2x+2x) expand that^

  2. ajprincess
    • 3 years ago
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    \(\cos4x=1-2\sin^2 2x\) \(\cos2x=1-2\sin^2x\) does that help?

  3. allison_
    • 3 years ago
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    It did, but could you please show me how cos 4x = 1 - 2 sin^2 2x?

  4. ajprincess
    • 3 years ago
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    ya sure. \(\cos4x=\cos(2x+2x)\) \(=\cos2x\cos2x-\sin2x\sin2x\) \(=\cos^2 2x-\sin^2 2x\) \(=1-\sin^2 2x-\sin^2 2x\) \((\cos^2 2x=1-\sin^2 2x)\) \(=1-2\sin^2 2x\)

  5. allison_
    • 3 years ago
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    Do you have a reference where it says cos^2 2x = 1−sin^2 2x? I think it would be useful for me since I have a formula sheet but I don't see that on here...

  6. ajprincess
    • 3 years ago
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    \(\cos^2x+\sin^2x=1\) Similarly \(\cos^2 2x+\sin^2 2x=1\) \(\cos^2 2x=1-\sin^2 2x\)

  7. allison_
    • 3 years ago
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    Thank you for your time and assistance. :)

  8. ajprincess
    • 3 years ago
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    Welcome:)

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