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Math Help - trig homework

  1. #1
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    trig homework

    I have two problems I need help with please.
    1. find the exact value of tan(2u) using double angle forumlas given tan(u)= -2/9, pi/2<u<pi

    2. use sum-to-product formulas to write the sum as a product?
    sin(5theta) - sin(theta)
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  2. #2
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    \tan(2u) = \frac{2\tan{u}}{1 - \tan^2{u}}

    substitute (-2/9) for tan(u) and do the arithmetic.


    \sin{a} - \sin{b} = 2\cos\left(\frac{a+b}{2}\right)\sin\left(\frac{a-b}{2}\right)<br />

    substitute 5\theta for a and \theta for b.
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