Results 1 to 5 of 5

Math Help - Help with checking Vector Question

  1. #1
    Newbie
    Joined
    May 2010
    Posts
    12

    Help with checking Vector Question

    Hey guys I am not sure if this is the right thread (can't seem to find one for vectors) but i am not sure if i'm on the right track here so i need some advice

    Question is:

    if \vec{a}=3i-2j , \vec{b}=-4i+4j , and \vec{c}=6i+-9j express the following vectors in their simplest form:

    (i) -5\vec{b}
    (ii) 2\vec{a}-\frac{1}{2}\vec{c}
    (iii) \frac{2}{3}\vec{a}-\frac{1}{2}\vec{b}-\frac{1}{4}\vec{c}

    My Solution:

    (i) -5\left(-4i+4j \right)=20i+\left(-20j \right)
    (ii) 2(3i-2j)-\frac{1}{2}(6i+(-9)j)
    = 6i-4j-3i+(-\frac{9}{2})j
    = (6-3=3i) -4j-\frac{9}{2}
    = -\frac{4}{1}-\frac{9}{2}
    =-\frac{8}{2}-\frac{9}{2}
    =-\frac{17}{2}

    Answer? 3i-\frac{17}{2}j

    (iii) \frac{2}{3}(3i-2j)-\frac{1}{2}(-4i+4j)-\frac{1}{4}(6i+(-9)j)
    (2i-\frac{4}{3}j)-(-2i+2j)-(\frac{3}{2}i+(-\frac{9}{4}j)
    2i+2i-\frac{3}{2}i
    = \frac{4}{1}i+\frac{3}{2}i
    = \frac{8}{2}+\frac{3}{2}
    =\frac{11}{2}i

    -\frac{4}{3}j+\frac{2}{1}j-\frac{9}{4}j
    = -\frac{16}{12}j+\frac{24}{12}j-\frac{27}{12}j
    = -\frac{19}{12}j

    Answer? \frac{11}{2}i-\frac{19}{12}j
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member
    Joined
    May 2010
    From
    Los Angeles, California
    Posts
    274
    Thanks
    1
    Looks Ok to me but you're presentation was hard to follow.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    May 2010
    Posts
    12
    Quote Originally Posted by ojones View Post
    Looks Ok to me but you're presentation was hard to follow.
    ah thank you! i'll write it better in my maths book and write it better next time i need help on here
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Senior Member
    Joined
    May 2010
    From
    Los Angeles, California
    Posts
    274
    Thanks
    1
    Actually, there is an arithmetic error in (ii): answer should be 3{\bf i}+(-4+\frac{9}{2}){\bf j}=3{\bf i}+\frac{1}{2}{\bf j}

    (iii) also has an error: you changed -\frac{3}{2}{\bf i} to \frac{3}{2}{\bf i} by mistake.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    May 2010
    Posts
    12
    Quote Originally Posted by ojones View Post
    Actually, there is an arithmetic error in (ii): answer should be 3{\bf i}+(-4+\frac{9}{2}){\bf j}=3{\bf i}+\frac{1}{2}{\bf j}

    (iii) also has an error: you changed -\frac{3}{2}{\bf i} to \frac{3}{2}{\bf i} by mistake.
    ah yea thanks! Great pickup!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Checking Vector Space Questions
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: September 9th 2010, 02:59 AM
  2. Green's theorem question needs checking
    Posted in the Calculus Forum
    Replies: 3
    Last Post: May 19th 2010, 07:42 AM
  3. Help with checking Vector Question
    Posted in the Trigonometry Forum
    Replies: 5
    Last Post: May 17th 2010, 01:22 AM
  4. checking answer for a Logarithm question
    Posted in the Math Topics Forum
    Replies: 2
    Last Post: February 19th 2010, 06:23 AM
  5. Question checking LaTeX output
    Posted in the LaTeX Help Forum
    Replies: 2
    Last Post: December 28th 2009, 10:26 PM

Search Tags


/mathhelpforum @mathhelpforum