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Math Help - Radian Measure and ANgles of the Cartesion question problem

  1. #1
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    Radian Measure and ANgles of the Cartesion question problem

    For the following value of cos \theta, determine the radian value of \theta

    a) -1/2

    First I found y from the equation r^2=x^2+y^2
    y= +- \sqrt{y}

    My graph therefore is in the 1 and 2 quadrant due to y having + and - values

    then i found inverse cos^-1 (1/2) = 1.05

    so: pi - 1.05 or 1.05

    However the answer according to the book is (4pi)/3
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  2. #2
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    Scratch this, I managed to figure it out. I forgot that cos is the x value and sin is the y value on the Cartesian Plane
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