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Math Help - How do you find theta when given secant?

  1. #1
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    Talking How do you find theta when given secant?

    we reviewed this in class but i really didnt understand it very well. :[ and now we were given a take home test on it...
    the problem is:
    If sec theta =5/2, and theta is in quadrant one, find he value of theta to the nearest minute.
    smeone please help!!
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  2. #2
    Member mathemagister's Avatar
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    Quote Originally Posted by DarkAngelxXxXx View Post
    we reviewed this in class but i really didnt understand it very well. :[ and now we were given a take home test on it...
    the problem is:
    If sec theta =5/2, and theta is in quadrant one, find he value of theta to the nearest minute.
    smeone please help!!
    secant is 1/cos

    So \frac{1}{\cos \theta} = \frac{5}{2}

    Can you do it now?
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  3. #3
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    so do yu just do
    cos theta = 2/5
    theta= (cos^-1)(2/5)
    theta= 1.159279....
    then theta =1 degree 9 minutes 33.406 seconds
    so the answer is 1 degree 9 minutes?
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  4. #4
    Member mathemagister's Avatar
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    Exactly, because that is already in quadrant one.

    EDIT: Thanks, HoI, of course your answer of 1.159... is in radians (which is in the first quadrant), sorry I automatically read your final answer in radians, too.
    Last edited by mathemagister; April 11th 2010 at 11:57 AM.
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  5. #5
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    Quote Originally Posted by DarkAngelxXxXx View Post
    so do yu just do
    cos theta = 2/5
    theta= (cos^-1)(2/5)
    theta= 1.159279....
    then theta =1 degree 9 minutes 33.406 seconds
    so the answer is 1 degree 9 minutes?
    Method is good, result is wrong! Your calculator is in radian mode. That is, arccos(2/5)= 1.159279... radians, not degrees.

    Either put your calculator in degree mode or change that answer to degrees by multiplying by \frac{180}{\pi}= \frac{180}{3.1415926}
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