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Math Help - Vectors (ii)

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    Vectors (ii)



    Can someone tell me how to arrive to the answer. 1/2(u + 3v)

    Thanks
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    Quote Originally Posted by r_maths View Post


    Can someone tell me how to arrive to the answer. 1/2(u + 3v)

    Thanks
    From the diagram it looks to me like BD = v... Something doesn't "add up" (if you don't mind the pun.)

    -Dan
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    Ah, sorry.

    BC not BD.

    (awful pun lol)
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    Quote Originally Posted by topsquark View Post
    From the diagram it looks to me like BD = v... Something doesn't "add up" (if you don't mind the pun.)
    I love that pun! Much funnier than all puns I make.
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    Am I right to say the arrows play a part into getting the answer?
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    Quote Originally Posted by r_maths View Post
    Am I right to say the arrows play a part into getting the answer?
    Yes. If you have the arrows backwards then you different answers when you find the vector sum.
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    Quote Originally Posted by r_maths View Post


    Can someone tell me how to arrive to the answer. 1/2(u + 3v)

    Thanks
    Hello,

    I've tried to get a solution of this problem and I failed very successfully

    Could it be that the proportion reads:

    AD : DC = 2 : 1 (?)

    If so, the solution is:

    1. AD = u + v

    2. AD = 2*DC ==> DC = (1/2)*AD

    3. BC = -u + AD + DC

    BC = -u + u+v + (1/2)*(u+v) = v + (1/2)*u + (1/2)*v = (1/2)*(u + 3v)
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    My apologies, it is AD : DC
    -
    Two mistakes in just copying out one question

    Thanks alot by the way.
    Last edited by r_maths; May 2nd 2007 at 07:09 AM.
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    Quote Originally Posted by r_maths View Post
    ...it is AC : DC
    ...
    Hi,

    now it's me who is really confused - because:

    AC = AD + DC. Therefore:

    AC/DC = 2 ==> AC = 2*DC ==> AD + DC = 2*DC ==> AD = DC

    From my previous post you know that

    BC = -u + AD + DC

    BC = -u + u+v + u+v = u + 2v

    This answer differs slightly( ) from the given answer.

    (Could it be that ... ahemm?)
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  10. #10
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    Lightning strikes 3 times....

    Its AD : DC

    Sorry sorry sorry
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