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Math Help - Prove sin and cos = 0

  1. #1
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    Prove sin and cos = 0

    Hi all,

    sin330cos150 - cos390sin390 = 0

    Prove:

    What am I to do with this? Do I convert ll to the one function or......mmmm got nothing.

    Any help would be appreciated.
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  2. #2
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    Quote Originally Posted by Joel View Post
    Hi all,

    sin330cos150 - cos390sin390 = 0

    Prove:

    What am I to do with this? Do I convert ll to the one function or......mmmm got nothing.

    Any help would be appreciated.
    Remember that the trig functions are periodic.

    cos(390)=cos(30)=\frac{\sqrt{3}}{2}

    sin(390)=sin(30)=\frac{1}{2}

    The other two values are:

    sin(330)=-\frac{1}{2}

    cos(150)=-\frac{\sqrt{3}}{2}

    If you don't see why these are true, look here: Trigonometric functions - Wikipedia, the free encyclopedia

    Scroll down and look at the unit circle next to the paragraph "Unit-circle definitions"
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  3. #3
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    so it would now look like....

    sin330cos150 - cos390sin390 = 0

    (- )(-√3/2) - ( )(√3/2) = 0
    √3/2 / 2 - √3/2 / 2 = 0 which is true


    Is this how i should set it out ?
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  4. #4
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    Yup
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