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Math Help - Quick trig question

  1. #1
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    Quick trig question

    Hi
    I need help on how to do this question:

    Find the value of \theta between 0 and 2\pi such that cos\theta = \frac{3}{5} and sin\theta = \frac{-4}{5}


    P.S
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  2. #2
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    Quote Originally Posted by Paymemoney View Post
    Hi
    I need help on how to do this question:

    Find the value of \theta between 0 and 2\pi such that cos\theta = \frac{3}{5} and sin\theta = \frac{-4}{5}


    P.S
    This is a 3-4-5 triangle, and the angle has to be in the fourth quadrant since cosine is positive and sine is negative.

    So \theta = 2\pi - \arccos{\frac{3}{5}}.

    You could also do \theta = 2\pi - \arcsin{\frac{4}{5}}.
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  3. #3
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    Quote Originally Posted by Prove It View Post
    This is a 3-4-5 triangle, and the angle has to be in the fourth quadrant since cosine is positive and sine is negative.

    So \theta = 2\pi - \arccos{\frac{3}{5}}.

    You could also do \theta = 2\pi - \arcsin{\frac{4}{5}}.

    I tried to do both ways and they get different answers.
    if you say they are the same shouldn't they get the same answer??
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