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Math Help - Vaules of Cos and Sin and stuff

  1. #1
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    Vaules of Cos and Sin and stuff

    Explain why the value of [cosX, sinX]*[cos(90+X), sin(90+X)] is independent of X.

    X=theta

    what does independent of X even mean?
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by stones44 View Post
    Explain why the value of [cosX, sinX]*[cos(90+X), sin(90+X)] is independent of X.

    X=theta
    i suppose you mean the dot product here? just take the dot product and use the addition formula for the functions in the second pair of brackets and simplify

    what does independent of X even mean?
    it means that it does not matter what X is, the value will be the same no matter what X we choose
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    ehhh im confused
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by stones44 View Post
    ehhh im confused
    \cos (A + B) = \cos A \cos B - \sin A \sin B

    \sin (A + B) = \sin A \cos B + \sin B \cos A

    now apply those identities, take the dot product and simplify. you will see that it does not matter what x is
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  5. #5
    Grand Panjandrum
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    Quote Originally Posted by stones44 View Post
    Explain why the value of [cosX, sinX]*[cos(90+X), sin(90+X)] is independent of X.

    X=theta

    what does independent of X even mean?
    Assuming dot product: if you simplify this properly you will have -\sin(x)\cos(x)+\cos(x)\sin(x) , which is?

    RonL
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