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Homework Help: Vector Gah

  1. Sep 7, 2005 #1
    Vector Gah!!!!

    Vector questions. Need help on these three.

    In ∆OAB, OA = a and OB = b. P is a point on AB such that BP:PA 1:2.
    Q is a point on the extension of OP such that OQ = 1.5OP

    a) Express BP and OP in terms of ‘a’ and ‘b’.
    these are the answers but how do they get it?
    BP = (1/3)(a - b)
    OP = (1/3)(a + 2b)

    b) Show that AQ = -0.5a + b
    i have no idea how to prove this

    c) Given that BQ = kOA, find the value of k.
    once again this is the answer but i dont know how to approach this can someone show me how to get this value thanks
    k = 0.5
  2. jcsd
  3. Sep 7, 2005 #2


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    Science Advisor
    Homework Helper

    Draw the vector that define the triangle. One side is made by the vector a, the other by b and the third by a-b. Then draw the points P and Q. From the drawing you can see that BP is one third the vector (a-b). The others are done similarly.
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