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P3 vectors.. eeeeeassy question!! watch

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    I must be doing something really stupid, but for some reason it's not working.

    P3 heinemann book page 192, question 53 part a)

    With respect to an origin, O, the position vectors of the points L and M are 2i - 3j + 3k and 5i + j + ck where c is a constant
    The point N is such that OLMN is a rectangle.

    find the value of c.

    Now surely with it being a rectangle, OL and OM must be perpendicular.
    therefore the dot product of these vectors must be 0.

    so 2i - 3j + 3k . 5i + j + ck
    10 - 3 + 3c = 0
    c = -7/3

    but the answer is 5! :confused: what the hell?
    It must be obvious, but I reckon I've lost it doing too much revision.. argh! help me out someone!
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    i've got the same as u.........maybe misprint in the book? as they always get answers wrong.....
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    (Original post by wonkey)
    i've got the same as u.........maybe misprint in the book? as they always get answers wrong.....

    but actually.......u never get fractions as an answer tho, the co-efficient is always an integer...hmmmm :confused:
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    Draw a diagram, OL and OM will not be perpendicular. OL and ON will.
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    The book is correct btw.
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    (Original post by JamesF)
    Draw a diagram, OL and OM will not be perpendicular. OL and ON will.
    but it's a rectangle? surely all the edges are at rightangles?
    can you please explain in more detail?
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    someone just explained this problem in another thread..look further down the page
 
 
 
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