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Math Help - Vector real simple question

  1. #1
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    Vector real simple question

    Only two simple questions
    (REally i am not good at math and i am in the 10th grade)
    This is my first post and hope to get some little help .In the summer i have tryed hacking now math has replaced hacking
    + or -
    First :



    Second : 2MN=6i how to solve this ?
    (MN and i are in vector with an index "-->")


    Note : if the post looks bad with the big picture i will replace that with a link
    Last edited by darklight; April 15th 2010 at 12:30 AM.
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  2. #2
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    Hello darklight

    Welcome to Math Help Forum!
    Quote Originally Posted by darklight View Post
    Only two simple questions
    (REally i am not good at math and i am in the 10th grade)
    This is my first post and hope to get some little help .In the summer i have tryed hacking now math has replaced hacking
    + or -
    1-
    Your first question asks how you should write
    \frac{-\vec a +3\vec b-2 \vec c}{7}, when \vec c= \binom 12
    Of the two answers you give, the one with the + sign is correct:
    \frac{-\vec a +3\vec b+ \binom{-2}{-4}}{7}
    since you have taken the - sign into account by mutliplying \binom12 by -2 to get \binom{-2}{-4}.

    Quote Originally Posted by darklight View Post
    2- 2MN=6i how to solve this ?
    (MN and i are in vector with an index "-->")
    Your question seems to ask: How do I solve
    2 -2\vec{MN} =6\vec i
    If so, it doesn't make sense, since 2 is a scalar and \vec{MN} and \vec i are vectors. You can't add vectors and scalars like this.

    What did you really mean?

    Grandad
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  3. #3
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    Thanks for the answers

    In the second question is my fault, didn't write that M(-3:-2) and N(x;y)
    I have to find the coordinates of N ?
    2MN=i
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  4. #4
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    Quote Originally Posted by darklight View Post
    Thanks for the answers

    In the second question is my fault, didn't write that M(-3:-2) and N(x;y)
    I have to find the coordinates of N ?
    2MN=i
    The wording of the question isn't clear to me so I'm just guessing:

    1. If M(-3, -2) and N(x, y) then

    \overrightarrow{MN} = (x, y)-(-3,-2)=(x+3 , y+2)

    2. If

    2 \overrightarrow{MN} = 6i (I'll trake the original version of the equation. See your 1st post) that means:

    (2x+6 , 2y+4) = (6,0)~\implies~\begin{array}{l}2x+6=6\\2y+4=0\end{  array}

    3. Solve these equations for x and y respectively. You'll get N(0, -2)
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  5. #5
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    thanks a lot ,this was what i asked for........
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