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Math Help - Trig Question Help

  1. #1
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    Trig Question Help

    Can someone please help me out with this question.


    Find all the possible angles for A if 0 ≤ A ≤ 2 (pi)

    I) cosA = -1/(square root of 2)



    How do I solve this? I'm really bad at this stuff and need to know because I have a test soon... I want to leanr how to do it but please explain how step by step.


    Thanks
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  2. #2
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    Consider this article. There is a 45-45-90 triangle

    Special right triangles - Wikipedia, the free encyclopedia

    Therefore using the cosine ratio \cos(\theta) = \frac{A}{H}

    For \cos(A) = \frac{-1}{\sqrt{2}}

    Consider this article

    http://www.haverford.edu/physics/Mat...Trig_Ident.pdf

    then A = 360 - 45, 180-45
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  3. #3
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    okay i have a totally unrelated question... I looked in my lesson and ifgured some stuff out but have trouble at one part...


    I know how to solve this question now... but when I draw the unit circle and draw the special triangle/angle or whatever you call it...


    How do i know what numbers are on the adjacent side, and opposite side.



    For the question: Cot A = -1/ square root of 3


    cot theta = x/y = -1/square root of 3


    then you find what x and y is to get the triangle.


    ---

    but for my question it's cos, so it's adj/hyp... so how do i figure out what numbers go at the adjacent, opposite and hyp when i draw the unit circle?


    I hope this makes some sense, I sort of understand it but get confused at this part.
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  4. #4
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    Quote Originally Posted by agent2421 View Post

    but for my question it's cos, so it's adj/hyp... so how do i figure out what numbers go at the adjacent, opposite and hyp when i draw the unit circle?
    The sides of the triangle should be considered on how they relate to the angle.

    The adjacent side links the angle in question to the right angle. The opposite side is opposite the angle and the hypotenuse is the longest side of the triangle.
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  5. #5
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    yes I know what they are but I'm trying to figure out what numbers should go for each side...

    For the question Cos A = -1 / square root of 2


    when I draw the unit circle and draw the special angle... what numbers would go at the adjacent, opposite and hyp side?


    Thanks for the help : )
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  6. #6
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    Special right triangles - Wikipedia, the free encyclopedia

    This article shows the sides of the triangle. The triangle fits onto the unit circle.
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  7. #7
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    thanks... I finally figured it out... wow I don't know how I didn't see that before... for some reason I thought it was always different the numbers for the 3 sides... I wasn't even thinking about the cases and how it's the same.


    Thanks again for all the help
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  8. #8
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    Hey i actually have one more question...

    When we look for the ratios for csc, sec and cot... say the angle is in Quadrant 2... does that mean that Sine is the only one that's positive and the otehr 2 will be negative?


    Becasue my teacher has an example and it might be wrong because it has only 1 of them being negative and the other 2 positive which is impossible right?
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