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Homework Help: Vector addition and subtraction. feeling stupid for being confused over this

  1. Nov 19, 2011 #1
    1. The problem statement, all variables and given/known data

    A = 2i + 3j
    B = -5i + 6j

    Calculate (draw vector diagram)
    A + B
    A - B
    2. Relevant equations

    actually we're just confused as to whether we need to use the angles to answer this or just answer it directly, meaning that for A + B the answer would be -3i + 9j

    3. The attempt at a solution

    do we use

    A + B = -3i + 9j

    or solve for the angles(*rounded off) and use

    A+B = ((√13)cos56 + (√61)cos50)i + ((√13)sin56 + (√61)sin50)j

  2. jcsd
  3. Nov 19, 2011 #2

    Simon Bridge

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    Try drawing the vectors on graph paper, and adding/subtracting head-to-tail.
    They are simple enough to do this, and it will clear up your confusion.

    The vectors are provided to you in Cartesian representation. If you do it by angles, you want the polar representation. These are entirely equivalent and will get you the same answers. (provided you worked out the angles correctly - yours are all in the 1st quadrant but the vectors are not... one is in the 4th quadrant so it's angle is greater than 270 degrees - I have not checked that you've accounted for this.)
    Last edited: Nov 19, 2011
  4. Nov 19, 2011 #3


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    Staff Emeritus
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    The problem statement asks you to 'draw vector diagram' for A+B and A-B. Did you do that?
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