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Homework Help: Introduction to Vectors

  1. Oct 24, 2009 #1
    1. The problem statement, all variables and given/known data

    If A, B, C, D are 4 points in a plane, then find ALL correct statements if AB=BC+CD

    A. AB is parallel to BD
    B. AB+BC=CD
    C. AB=BD
    D. AB−BC=BD
    E. none of the above

    [Note: The answer could be more than one option]

    2. Relevant equations


    3. The attempt at a solution

    I'm not quite sure how to do this question, even though it seems easy. I'm thinking option C and D but it's wrong. I'm pretty much doing guess work here because my instructor didn't explain it.

    Can I get some help here? Thanks in advance.
  2. jcsd
  3. Oct 24, 2009 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    Why do you think it's C and D?
  4. Oct 24, 2009 #3
    After some consideration, I think D is incorrect. But I chose C because a friend told me to use the parallelogram sum rule (AR = AP + PR).

    So my new guess would be just C. I'm not sure how to check A though.
  5. Oct 24, 2009 #4


    Staff: Mentor

    For A, draw a line segment from B to C, then draw another line segment from C to D. Then you know that BD = BC + CD. You're given that AB = BC + CD. Can you conclude anything from these two equations?
  6. Oct 24, 2009 #5


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    Science Advisor

    From AB= BC+ CD, subtracting BC from both sides, you get AB- BC= CD, not BD.

    Yes, vector addition can be visualized as the "parallelogram rule". That gives the correct answer.
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