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Math Help - Trigonometry Assistance

  1. #1
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    Trigonometry Assistance

    If sin A = -sqrt(17)/9 and A is in the 3rd quadrant, find exact values of:

    (i) cos A (ii) tan A (iii) sin 2A


    I guess im sort of confused what is being asked, the way I attempted it was:


    Assuming Sin A = -sqrt(17)/9
    Then A = Arcsin( -sqrt(17)/9)
    Then A = -.476

    SO

    (i) cos(-.476) = .889
    (ii) tan(-.476) = -.515
    (iii) sin(-.952) = -.814

    Am I anywhere near close on this one ?, Thanks in advance for any help.
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  2. #2
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    Re: Trigonometry Assistance

    Do you answers seem reasonable, considering that you are told your angle is in the THIRD quadrant?

    You are expected to use Trigonometric Identities to solve these problems. What identities do you think would be appropriate?
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