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    QUESTION ATTACHED

    Can someone please explain to me how they got OC = 2AB

    I have the following;

    OC = OA + AB + BC

    OA = a and AB = b - a

    I just can't visualise it at all
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    Zacken
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    (Original post by rache11ouise)
    QUESTION ATTACHED

    Can someone please explain to me how they got OC = 2AB

    I have the following;

    OC = OA + AB + BC

    OA = a and AB = b - a

    I just can't visualise it at all
    Look at the line AB, now try and mentally drag it so A start from O and it moves in the diagonal upward right direction so that B is now at the centre. If you double this length, B kind of goes to C, can you see what I mean or should I explain more?
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    (Original post by rache11ouise)
    QUESTION ATTACHED

    Can someone please explain to me how they got OC = 2AB

    I have the following;

    OC = OA + AB + BC

    OA = a and AB = b - a

    I just can't visualise it at all
    In addition to what Zacken has said, if you draw a line from A to the centre of the hexagon (call it M) then it's clear by looking at the parallelogram ABCM that AB = MC.

    And so OC = 2AB.
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    How would I know to do that in the exam though, now you've pointed it out i can see that OC = 2AB because the diagram is to scale but I still don't really know why you have to do it that way. Am i making sense? could you please explain why you did what you did...
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    (Original post by rache11ouise)
    How would I know to do that in the exam though, now you've pointed it out i can see that OC = 2AB because the diagram is to scale but I still don't really know why you have to do it that way. Am i making sense? could you please explain why you did what you did...
    The longest diagonal of a regular hexagon is always twice the length of the side.

    Another way:

    Call M the centre of the circle. Do you accept that \overrightarrow{MB} = \boldsymbol{a}?

    Then \overrightarrow{OM} = \overrightarrow{OB} + \overrightarrow{BM} = \boldsymbol{b} - \boldsymbol{a}

    So \overrightarrow{OC} = 2\overrightarrow{OM} = 2(\boldsymbol{b}-\boldsymbol{a})
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    (Original post by rache11ouise)
    How would I know to do that in the exam though, now you've pointed it out i can see that OC = 2AB because the diagram is to scale but I still don't really know why you have to do it that way. Am i making sense? could you please explain why you did what you did...
    That's what the point of practice is. Now that you've learnt and (hopefully) understood this, you should be able to do it in an exam.
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    Thankyou I can see it now, I think I just need some more practice. Have you come across any particularly difficult questions on vectors or any similar to this whilst revising? Im currently going through the worksheets on mathsandphysicstutor. Are vectors a problem for anyone else? I seem fine with most of the topic, I've just always struggled with vectors
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    (Original post by rache11ouise)
    Thankyou I can see it now, I think I just need some more practice. Have you come across any particularly difficult questions on vectors or any similar to this whilst revising? Im currently going through the worksheets on mathsandphysicstutor. Are vectors a problem for anyone else? I seem fine with most of the topic, I've just always struggled with vectors
    how difficult do you want?
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    (Original post by rache11ouise)
    Thankyou I can see it now, I think I just need some more practice. Have you come across any particularly difficult questions on vectors or any similar to this whilst revising? Im currently going through the worksheets on mathsandphysicstutor. Are vectors a problem for anyone else? I seem fine with most of the topic, I've just always struggled with vectors
    To be honest, this question is GCSE level if you spot that OC = 2AB.

    C4 vectors exam questions are usually nothing like this. Have you tried past paper questions? If you're struggling with a certain past paper question then you're welcome to post it here.
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    (Original post by drandy76)
    how difficult do you want?
    Im fine with most vector questions its just the ones involving visualising and diagrams that I struggle with, the algebra and equation manipulation i kind quite easy. I just struggle with the diagrams so I'm looking for the hardest question involving diagrams, please. If you find any would you be able to link me to them please
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    (Original post by notnek)
    To be honest, this question is GCSE level if you spot that OC = 2AB.

    C4 vectors exam questions are usually nothing like this. Have you tried past paper questions? If you're struggling with a certain past paper question then you're welcome to post it here.
    I can't remember ever studying vectors at GCSE maybe thats why I have this gap in my knowledge. I find questions with diagrams the only ones I struggle with, I've always had problems visualising things. The exam questions I've completed don't seem to involve many diagrams but I'm worried if i don't practice this area of vectors using diagrams that it could underpin all my other knowledge
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    (Original post by rache11ouise)
    Im fine with most vector questions its just the ones involving visualising and diagrams that I struggle with, the algebra and equation manipulation i kind quite easy. I just struggle with the diagrams so I'm looking for the hardest question involving diagrams, please. If you find any would you be able to link me to them please
    I like a few of theseName:  ImageUploadedByStudent Room1457688341.026104.jpg
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