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    The angle q is greater than 90° and less than 360° and cos q = 2/3.
    Find the exact value of tan q.
    Right I got tan q =  \frac{\sqrt 5}{2}
    But how do I now use the CAST diagram to find the exact value of . I know the answer is tan q = - \frac{\sqrt 5}{2} but I can't see how the diagram shows this.

    Well you know it's between 90 and 360, so (if my memory of the diagram is right) that puts it in the C, S or T section, and since cosq is positive it must be in the C quadrant, which tells you the sign of tanq.
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Updated: September 24, 2010

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