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Math Help - One Half-Angle Queston

  1. #1
    Junior Member CONFUSED_ONE's Avatar
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    One Half-Angle Queston

    Question...
    For the Half-Angle Problems:

    how do you know if the answer is positve or negative...
    (i circled it in RED)
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    Quote Originally Posted by CONFUSED_ONE
    Question...
    For the Half-Angle Problems:

    how do you know if the answer is positve or negative...
    (i circled it in RED)
    It depends in which quadrant is \frac{a}{2}.
    NOT a but \frac{a}{2}.

    If \frac{a}{2} is in the first or second quadrant then you use positive, otherwise use the negative.
    Your question, is a classic mistake which I seen many people make, hopefully you will not make it.
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    for example, what if a=4/5. so it'll be (4/5)/2 and that'll turn out to be 2/5. how do i know if 2/5 is in the first or second quadrant?
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    Quote Originally Posted by CONFUSED_ONE
    for example, what if a=4/5. so it'll be (4/5)/2 and that'll turn out to be 2/5. how do i know if 2/5 is in the first or second quadrant?
    I presume that is in radians?
    The first and second quadrant span 0^o\leq x\leq 180^o
    Or in Radians, 0\leq x\leq \pi
    Since,
    0\leq .4\leq 3.14 it is in the first and second quadrants.

    In fact it is in first quadrant because it spans,
    0\leq x\leq \frac{\pi}{2}\approx 1.57
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