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Math Help - Prove these identities.

  1. #1
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    Prove these identities.

    cos(5w) + cos(w) cot(2w)
    ----------------- = ----------
    cos(w) - cos(5w) tan(3w)

    and

    cos^2(1/2x) - sin^2 (1/2x) = cosx

    Lol alright.

    For the 1st one. I just used a sum product identity on the left side of the equation, but came up with just cot(2w) * cot(3w). Am I missing something?

    and for the 2nd one, I don't know what identity to use lol
    Last edited by hellojellojw; July 20th 2009 at 08:39 PM.
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  2. #2
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    Krizalid's Avatar
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    Quote Originally Posted by hellojellojw View Post

    Show steps please. Thanks!
    No.

    I think you can change that sentence by rewritting it as "show hints please!" Or show what have you done.
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  3. #3
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    Quote Originally Posted by Krizalid View Post
    No.

    I think you can change that sentence by rewritting it as "show hints please!" Or show what have you done.
    Okay, I understand.
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  4. #4
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    For the 1st one. I just used a sum product identity on the left side of the equation, but came up with just cot(2w) * cot(3w). Am I missing something?
    You're very close.
    \cot 2w \cot 3w = \frac{\cot 2w}{\tan 3w}. Remember that tangent and cotangent are reciprocals?

    and for the 2nd one, I don't know what identity to use lol
    Try the cosine of a double angle formula.


    01
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  5. #5
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    Quote Originally Posted by yeongil View Post
    You're very close.
    \cot 2w \cot 3w = \frac{\cot 2w}{\tan 3w}. Remember that tangent and cotangent are reciprocals?


    Try the cosine of a double angle formula.


    01
    oh wow didn't notice that before. Thanks
    For the cosine double angle formula, do I need to show steps? I mean it looks the same, its just theta divided by 2.
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  6. #6
    No one in Particular VonNemo19's Avatar
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    Quote Originally Posted by hellojellojw View Post
    oh wow didn't notice that before. Thanks
    For the cosine double angle formula, do I need to show steps? I mean it looks the same, its just theta divided by 2.
    When proving something, always show steps, or at least make note of them.
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