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Math Help - tan ,cos

  1. #1
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    tan ,cos

    tan A = -21/20

    90 degrees< A < 180 degrees (meaning in QII)

    find cos

    Is it -20?
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  2. #2
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    Quote Originally Posted by daydreembelievr View Post
    tan A = -21/20

    90 degrees< A < 180 degrees (meaning in QII)

    find cos

    Is it -20?
    Obviously not since (and you should know this) -1 \leq \cos A \leq 1.

    Hint: \sqrt{21^2 + 20^2} = 29.
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  3. #3
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    ..No

    Quote Originally Posted by daydreembelievr View Post
    tan A = -21/20

    90 degrees< A < 180 degrees (meaning in QII)

    find cos

    Is it -20?


    No remember
    -1=<sinx=<1
    &
    -1=<cosx=<1

    cos=\frac{20}{\sqrt(20^2+ (-21)^2} =\frac{20}{\sqrt841}
    cos is negative in QII so put a (-) sign
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