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Math Help - how do I do this trig addition formula problem?

  1. #1
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    how do I do this trig addition formula problem?

    Angle A is acute.
    I have a list of trig formulas

    here is the problem...
    19. If sin A = 5/13, find sin 2A and cos 2A
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  2. #2
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    Quote Originally Posted by RaphaelB30 View Post
    Angle A is acute.
    I have a list of trig formulas

    here is the problem...
    19. If sin A = 5/13, find sin 2A and cos 2A
    \cos(2A) = 1 - 2\sin^2{A}

    \sin(2A) = 2\sin{A}\cos{A} ... use a reference triangle or the Pythagorean identity to find \cos{A}
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  3. #3
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    Quote Originally Posted by RaphaelB30 View Post
    Angle A is acute.
    I have a list of trig formulas

    here is the problem...
    19. If sin A = 5/13, find sin 2A and cos 2A
    sin(x) = opp/hyp so you construct a right angled triangle with the opposite 5 and hypotenuse 13. You can then find the adjacent side easily enough and thus find cos(x).

    For sin(2A) and cos(2A) use an identity
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