Results 1 to 10 of 10

Math Help - Vector Problems

  1. #1
    Super Member
    Joined
    Dec 2008
    Posts
    509

    Vector Problems

    Hi
    Need help on the following questions:
    1)

    Find the terms of a and b:
    i) \vec{OD}
    ii) \vec{DC}
    iii) \vec{DE}

    2)In the following case find the vector resolutes of the first vector parallel to and perpendicular to the second vector.
    a=2i-2j+k
    b=i+j+4k

    P.S
    Follow Math Help Forum on Facebook and Google+

  2. #2
    No one in Particular VonNemo19's Avatar
    Joined
    Apr 2009
    From
    Detroit, MI
    Posts
    1,823
    Quote Originally Posted by Paymemoney View Post
    Hi
    Need help on the following questions:
    1)

    Find the terms of a and b:
    i) \vec{OD}
    ii) \vec{DC}
    iii) \vec{DE}

    2)In the following case find the vector resolutes of the first vector parallel to and perpendicular to the second vector.
    a=2i-2j+k
    b=i+j+4k

    P.S
    Have you tried anything? Is your trouble with the concept of vectors in their component forms? Or, is it with the concept of when vector are cosidered to be orthoganal? If you were to show some work or ask a question, I could help you.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member
    Joined
    Dec 2008
    Posts
    509
    ok well i tired the first two and i got \vec{OD}=2a+3b and \vec{DC}=2a+4b.
    I don't understand why this is incorrect, would you care to explain?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,492
    Thanks
    1393
    Quote Originally Posted by Paymemoney View Post
    ok well i tired the first two and i got \vec{OD}=2a+3b and \vec{DC}=2a+4b.
    I don't understand why this is incorrect, would you care to explain?
    Please show HOW you got these answers...
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Super Member
    Joined
    Dec 2008
    Posts
    509
    well i looked at the diagram and counted the squares for a and b.

    oops i forgot to add that \vec{OA}=a and \vec{OB}=b
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,492
    Thanks
    1393
    Well if you look at the grid, you'll see that 2 squares across = \mathbf{b} and 1 square up = \mathbf{a}.

    Since OD is 3 squares across, wouldn't it mean 1.5\mathbf{b}? And then to go 2 squares up you would need to add 2\mathbf{a}?

    So OD = 2\mathbf{a} + 1.5\mathbf{b}.

    Now have a think about the others.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,546
    Thanks
    1395
    Quote Originally Posted by Paymemoney View Post
    Hi
    Need help on the following questions:
    1)

    Find the terms of a and b:
    i) \vec{OD}
    ii) \vec{DC}
    iii) \vec{DE}
    What are a and b? Do you mean the coordinate vectors i and j? Or do you mean OA and OB?

    2)In the following case find the vector resolutes of the first vector parallel to and perpendicular to the second vector.
    a=2i-2j+k
    b=i+j+4k

    P.S
    I gave you the formula here:
    http://www.mathhelpforum.com/math-he...resolutes.html
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Super Member
    Joined
    Dec 2008
    Posts
    509
    Quote Originally Posted by HallsofIvy View Post
    What are a and b? Do you mean the coordinate vectors i and j? Or do you mean OA and OB?


    I gave you the formula here:
    http://www.mathhelpforum.com/math-he...resolutes.html
    I mean OA and OB.

    yeh, but i get the wrong answer:
    This is what i have done:
    (2i-2j+k) \cdot (\frac{i-j-4k}{\sqrt6})(\frac{i-j-4k}{\sqrt6})

    (\frac{2+2-4}{\sqrt6})(\frac{i-j-4k}{\sqrt6})
    Follow Math Help Forum on Facebook and Google+

  9. #9
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,546
    Thanks
    1395
    Quote Originally Posted by Paymemoney View Post
    I mean OA and OB.

    yeh, but i get the wrong answer:
    This is what i have done:
    (2i-2j+k) \cdot (\frac{i-j-4k}{\sqrt6})(\frac{i-j-4k}{\sqrt6})
    But you gave the second vector as i+j- 4k, not i- j- 4k

    (\frac{2+2-4}{\sqrt6})(\frac{i-j-4k}{\sqrt6})
    Follow Math Help Forum on Facebook and Google+

  10. #10
    Super Member
    Joined
    Dec 2008
    Posts
    509
    sorry about that, i made some typos.
    Let me do it again, This is my full solution, according to the book's answers is incorrect.
    a=2i-2j+k
    b=i+j+4k

    =a \cdot \vec{b}(\vec{b})
    =2i-2j+k \cdot (\frac{i+j+4k}{\sqrt6})(\frac{i+j+4k}{\sqrt6})
    =\frac{4}{\sqrt6}(\frac{i+j+4k}{\sqrt6})

    =\frac{4i}{6}+\frac{4j}{6}+\frac{16k}{6}

    =\frac{4}{6}(i+j+4k)

    Now the answers says its \frac{2}{9}(i+j+4k)

    I Hope this time i make sense.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Vector problems
    Posted in the Pre-Calculus Forum
    Replies: 6
    Last Post: August 27th 2011, 08:32 PM
  2. vector problems
    Posted in the Calculus Forum
    Replies: 1
    Last Post: September 5th 2009, 12:37 AM
  3. Two vector problems I need some help with
    Posted in the Pre-Calculus Forum
    Replies: 9
    Last Post: August 19th 2009, 04:30 PM
  4. vector problems
    Posted in the Calculus Forum
    Replies: 2
    Last Post: September 12th 2008, 03:12 AM
  5. vector problems
    Posted in the Advanced Applied Math Forum
    Replies: 1
    Last Post: March 4th 2008, 10:21 AM

Search Tags


/mathhelpforum @mathhelpforum