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Thread: Trig identity proof

  1. #1
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    Trig identity proof

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

    to prove that $\displaystyle \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. #2
    MHF Contributor red_dog's Avatar
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    $\displaystyle \sin A+\sin B=2\sin\frac{A+B}{2}\cos\frac{A-B}{2}$

    $\displaystyle \cos A+\cos B=2\cos\frac{A+B}{2}\cos\frac{A-B}{2}$
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  3. #3
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    Quote Originally Posted by red_dog View Post
    $\displaystyle \sin A+\sin B=2\sin\frac{A+B}{2}\cos\frac{A-B}{2}$

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

    Thank you.
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