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Math Help - Vector triangle help

  1. #1
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    Vector triangle help

    Okay, so first time on the site. Let's hope this goes well, lol.

    The question: Find, correct to the nearest degree,the three angles of the triangle with the given vertices.
    The vertices: A(1,0), B(3,6), C(-1,4)

    So I tried to start it out. Drew it because visuals rock. Then I found the distances between the points.

    AB= \sqrt{40}
    BC= \sqrt{20}
    CA= \sqrt{20}

    That's about as far as I was able to go. Any help is appreciated. Thanks!

    ~Cen
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  2. #2
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    m\left( {\angle ABC} \right) = \arccos \left( {\frac{{\overrightarrow {BA}  \cdot \overrightarrow {BC} }}{{\left\| {\overrightarrow {BA} } \right\|\left\| {\overrightarrow {BC} } \right\|}}} \right)<br />
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  3. #3
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    Ok, I slightly get what you're saying but how would I find the magnitude of BC and BA?
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  4. #4
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    Quote Originally Posted by Centara View Post
    Ok, I slightly get what you're saying but how would I find the magnitude of BC and BA?
    You did it in the original post.
    The length of the vector(BA) is the length of the line segment BA.

    Do you know how to find the vector(BA)?
    Do you know how to find dot products?
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  5. #5
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    I have no idea how to find vector BA. We kind of just started this stuff last week and I'm trying to understand it all but I'm getting so caught up it's insane.

    I can do dot products. That's simple. Is that how you find BA? It'd be my luck it is, lol.
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  6. #6
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    Quote Originally Posted by Centara View Post
    I have no idea how to find vector BA. We kind of just started this stuff last week and I'm trying to understand it all but I'm getting so caught up it's insane. I can do dot products. That's simple. Is that how you find BA? It'd be my luck it is, lol.
    You are not ready for this task.
    It is a sad statment on education that you are asked to do this.
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  7. #7
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    Quote Originally Posted by Centara View Post
    Okay, so first time on the site. Let's hope this goes well, lol.

    The question: Find, correct to the nearest degree,the three angles of the triangle with the given vertices.
    The vertices: A(1,0), B(3,6), C(-1,4)

    So I tried to start it out. Drew it because visuals rock. Then I found the distances between the points.

    AB= \sqrt{40}
    BC= \sqrt{20}
    CA= \sqrt{20}

    That's about as far as I was able to go. Any help is appreciated. Thanks!

    ~Cen
    Do you know the cosine rule? Since you know the lengths of the sides of the triangle, that will enable you to calculate the angles.
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  8. #8
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    Okay, I finally realized what I was missing. There was a whole section of notes I was skipping over that had the formulas I was looking for. Same one Plato gave me but with the notation that I needed to remember how to find the vectors for BA and BC. Thanks guys!!!
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