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  • 1 Post By Shakarri

Math Help - trigonometry !! a very tricky trick

  1. #1
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    trigonometry !! a very tricky trick

    hey there

    regarding this problem

    i know that i can use the cosine law and then the sine law to investigate whether the other ange must be 45 or not,,
    but it takes alot of time and i kinda don't have that much time to solve a problem!!

    i don't know if am overlooking other way of doing it??
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  2. #2
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    Re: trigonometry !! a very tricky trick

    I assume you are trying to show if this is true or false. You will have to use the cosine rule then the sine rule but to save yourself a bit of work think about whether the angle \frac{\pi}{4} will be opposite the side with length 4 or 8.
    Last edited by Shakarri; September 7th 2013 at 01:32 PM.
    Thanks from topsquark
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  3. #3
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    Re: trigonometry !! a very tricky trick

    You can solve this without the law of cosines if you note that 180 - 60 - 45 = 75 and 75 - 30 = 45.
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  4. #4
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    Re: trigonometry !! a very tricky trick

    emakarov,, i didn't really get how could that help me,,

    may you please eleborate on that??
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  5. #5
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    Re: trigonometry !! a very tricky trick

    Let angle A be 60, AB = 4 and AC = 8. If angle C is 45, then angle B is 75. Draw the altitude BH. Then angle CBH is 45, i.e., BH = HC. Can you finish?
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  6. #6
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    Re: trigonometry !! a very tricky trick

    I understand the problem like this:

    one side = 4
    adjacent side = 8
    angle between them = 60 deg

    this is a half equilateral triangle. One angle is 90 deg and the other is 30 deg. I think pi/4 in the original question is incorrect, or the given sided lengths are not 4 and 8. The triangle of the original question does not exist.
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