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Thread: Trig identity proof

  1. January 18th 2010, 06:28 AM #1
    Tweety
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    Trig identity proof

    Use the indenities; (sinA+sinB) and (cosA+cosB)

    to prove that \frac{sin2x+sin2y}{cos2x+cos2y} = tan(x+y)

    I am really stuck on this, as the question is not clear to me. Is it talking about the addition formula? sin(A+B).
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  2. January 18th 2010, 06:41 AM #2
    red_dog
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    \sin A+\sin B=2\sin\frac{A+B}{2}\cos\frac{A-B}{2}

    \cos A+\cos B=2\cos\frac{A+B}{2}\cos\frac{A-B}{2}
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  3. January 18th 2010, 06:46 AM #3
    Tweety
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    Quote Originally Posted by red_dog View Post
    \sin A+\sin B=2\sin\frac{A+B}{2}\cos\frac{A-B}{2}

    \cos A+\cos B=2\cos\frac{A+B}{2}\cos\frac{A-B}{2}
    Oh I am suppose to be using those formulas, got it now!

    Thank you.
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