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    2. The points A and B have position vectors 3i − 2j + k and −i + 2j − 7k.
    Find position vector of the point P on AB such that
    AP : P B = 3 : 1
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    (Original post by sk9898)
    2. The points A and B have position vectors 3i − 2j + k and −i + 2j − 7k.
    Find position vector of the point P on AB such that
    AP : P B = 3 : 1
    What have you done so far? Do you have a method for this?
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    (Original post by ghostwalker)
    What have you done so far? Do you have a method for this?
    ive worked out what AB is
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    (Original post by sk9898)
    ive worked out what AB is
    Good. So, what fraction of the way along AB is P going to be?
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    (Original post by ghostwalker)
    Good. So, what fraction of the way along AB is P going to be?
    3/4
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    (Original post by sk9898)
    3/4
    Yep. So AP = (3/4) AB

    Then the position vector of P, that is OP, is simply OA + AP.
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    (Original post by ghostwalker)
    Yep. So AP = (3/4) AB

    Then the position vector of P, that is OP, is simply OA + AP.
    so we do the opposite and add
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    (Original post by sk9898)
    so we do the opposite and add
    I can't interpret that sentence in any meaningful way. You'll have to elaborate on what you mean.
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    (Original post by sk9898)
    so we do the opposite and add
    final answer i got is j-5k or 0i+j-5k
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    (Original post by sk9898)
    final answer i got is j-5k or 0i+j-5k
    Agreed.
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    (Original post by ghostwalker)
    Agreed.
    thanks.

    there is another question that i need help with.

    Given three nonzero vectors a, b and c, are the following statements True or False? Give a short reason or counter-example to justify your answer.
    (a) If a ⊥ b and also b ⊥ c then a ⊥ c.
    (b) If a ⊥ b and also a ⊥ c then a ⊥ (b + c).
    (c) If a ⊥ b and also b ⊥ c then b ⊥ (a − c).
    (d) If a ⊥ (b + c) and also a ⊥ (b − c) then a ⊥ b.
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    (Original post by sk9898)
    thanks.

    there is another question that i need help with.

    Given three nonzero vectors a, b and c, are the following statements True or False? Give a short reason or counter-example to justify your answer.
    (a) If a ⊥ b and also b ⊥ c then a ⊥ c.
    (b) If a ⊥ b and also a ⊥ c then a ⊥ (b + c).
    (c) If a ⊥ b and also b ⊥ c then b ⊥ (a − c).
    (d) If a ⊥ (b + c) and also a ⊥ (b − c) then a ⊥ b.
    Have to leave that for someone else, as I've other things to be doing, and that's going to take a while. Do post your thoughts, what you've tried, etc. as per the forum guidelines.
 
 
 
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