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C4 Vectors HELP PLEASE!

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    Confusing issue on vectors for tomorrow,
    When you need to find out an angle, do the direction of the vectors need to be facing the way relative to the angle???

    E.g.
    If there are the position vectors A, B and C and we need to work out angle ABC,
    do we use AB with CB/BA with BC seeing as each pair go into or out of the angle???

    I was taught that they must both be either coming out of the angle or going into the angle but some exams have them both going the same direction!!!

    E.g. Look at the OCR Jan10 question 2 and markscheme: http://www.ocr.org.uk/download/pp_10...n_gce_4724.pdf / http://www.ocr.org.uk/download/ms_10...10_gce_jan.pdf

    THANKS!
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    Huh, can't see the documents.

    Yes, they must both be going in or both be going out when you're using the angle for things such as dot/cross product. I think both-out is the standard definition, while both-in is just the vertical angle of both-out. If the vectors are tip-to-tail, then you'll find the supplementary angle instead. In some cases, such as when two lines are intersecting (you don't know which angle they're talking about), they'll ask you for the acute/obtuse angle.

    In triangles, you have to use AB and CB or BA and BC to find the interior angles. Otherwise, you'll be finding the exterior angle.
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    (Original post by aznkid66)
    Huh, can't see the documents.

    Yes, they must both be going in or both be going out when you're using the angle for things such as dot/cross product. I think both-out is the standard definition, while both-in is just the vertical angle of both-out. If the vectors are tip-to-tail, then you'll find the supplementary angle instead. In some cases, such as when two lines are intersecting (you don't know which angle they're talking about), they'll ask you for the acute/obtuse angle.

    In triangles, you have to use AB and CB or BA and BC to find the interior angles. Otherwise, you'll be finding the exterior angle.
    Sorry, I've updated the link.

    Yeah that's exactly what I thought, but it doesn't appear right in the mark scheme nor in this video tutorial on youtube http://youtu.be/NeV8eyJgCis?hd=1. Really confused with this and a tad panicked.
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    BUMP?
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    They don't seem to ignore this in question 2.
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    both going in or both going out
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    For that question in particular, does it work if you do it the right way instead of having on going into the angle and one going out? I'm not sure if I've made a mistake somewhere just want someone to confirm

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Updated: June 20, 2012
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