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Math Help - [SOLVED] finding sin s

  1. #1
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    [SOLVED] finding sin s

    cot s = -1/3, s in quadrant IV
    what is sin s in quadrant IV?

    well..
    cot s= cos s/sin s
    since it's quadrant IV, cos is + and sin is -
    -1/3 = 1/-3
    sin s= -3

    is this correct? i think i'm doing it right.
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  2. #2
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    Hello somanyquestions
    Quote Originally Posted by somanyquestions View Post
    cot s = -1/3, s in quadrant IV
    what is sin s in quadrant IV?

    well..
    cot s= cos s/sin s
    since it's quadrant IV, cos is + and sin is -
    -1/3 = 1/-3
    sin s= -3

    is this correct? i think i'm doing it right.
    You need to use Pythagoras' Theorem to find the length of the third side:
    \cot s = \frac{\text{Adjacent}}{\text{Opposite}}
    = (-)\frac{1}{3} (I've put the minus sign in brackets, because at this stage we don't need to worry about it.)
    \Rightarrow \text{Hypotenuse}^2 = 1^2+3^2
    =10
    \Rightarrow\text{Hypotenuse}=\sqrt{10}
    So we can now say:
    \sin s = \pm\frac{\text{Opposite}}{\text{Hypotenuse}}
    =\pm\frac{3}{\sqrt{10}}
    Now we can look at the sign of sine in QIV (as you correctly did), and say:
    \sin s = -\frac{3}{\sqrt{10}}
    Grandad
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  3. #3
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    Wow, Thanks! You've made this a lot clearer for me.
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