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Math Help - Simple vector problem

  1. #1
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    Simple vector problem

    1) given OP = (4, -2, 1) and OQ = (2, 4, 4) Find PQ.

    I think I got this right, I got PQ = (6, 2, 5) with magnitude (65)^0.5 ??

    2) given OP = (7, -2, 3) and PQ = (0, 3, -4), find OQ

    I got OQ = (7, 5, -7)

    3) point P = (1, 2, 3), find points R and Q such that a = PQ and b=PR and obtain the vector QR

    I would appreciate someones input/help on this as I'm not entirely sure how to do it
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  2. #2
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  3. #3
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    Quote Originally Posted by a8281333 View Post
    1) given OP = (4, -2, 1) and OQ = (2, 4, 4) Find PQ.

    I think I got this right, I got PQ = (6, 2, 5) with magnitude (65)^0.5 ??
    NO. If you draw a picture you will see that you can "follow the arrows" from O to P (using vector OP) then from P to Q (using vector PQ. That is the same as saying that OQ= OP+ PQ. PQ= OQ-OP. Subtract, don't add.

    2) given OP = (7, -2, 3) and PQ = (0, 3, -4), find OQ
    I got OQ = (7, 5, -7)
    Same basic argument: OQ= OP+ PQ so now you add rather than subtract.


    3) point P = (1, 2, 3), find points R and Q such that a = PQ and b=PR and obtain the vector QR

    I would appreciate someones input/help on this as I'm not entirely sure how to do it
    You are given the single point P. Are you not given a and b? If so, just choose R and Q to be any points you want! Then PQ+ QR= PR so QR= PR- PQ= b- a.
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  4. #4
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    sorry, a = 3i + j - k and b = -2i + 3j

    i got for 1) (-2,6,3) and |PQ| = 7 which made sense when i drew the diagram

    for 2) i got (7,1,-1)
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