1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Finding norm of some vectors

  1. Mar 5, 2013 #1
    1. The problem statement, all variables and given/known data

    [itex]u=(2,-2,3)[/itex]
    [itex]v=(1,-3,4)[/itex]
    [itex]w=(3,6,-4)[/itex]

    1.
    [itex]\left \| 2u-4v+w \right \|[/itex]

    2.
    [itex]\left \| u \right \|-\left \| v \right \|[/itex]


    3. The attempt at a solution

    1.
    [itex]\left \| 2(2,-2,3)-4(1,-3,4)+(3,6,-4) \right \|[/itex]
    [itex]\left \| (4,-4,6)+(-4,12,-16)+(3,6,-4) \right \|[/itex]
    [itex]\left \| (3,14,-14)\right \|[/itex]

    [itex]=\sqrt{3^{2}+14^{2}+(-14)^{2}}[/itex]
    [itex]=\sqrt{9+196+196}[/itex]
    [itex]=\sqrt{401}[/itex]

    answer in book is [itex]\sqrt{529}[/itex]

    2.
    [itex]\left \| (2,-2,3) \right \|-\left \| 1,-3,4 \right \|[/itex]
    [itex]\sqrt{2^{2}+(-2)^{2}+3^{2}}-\sqrt{1^{2}+(-3)^{2}+4^{2}}[/itex]
    [itex]\sqrt{4+4+9}-\sqrt{1+9+16}[/itex]
    [itex]\sqrt{17}-\sqrt{26}[/itex]

    answer in book is [itex]\sqrt{26}[/itex]
     
  2. jcsd
  3. Mar 5, 2013 #2

    HallsofIvy

    User Avatar
    Science Advisor

    Your work is correct.

    I see three possibilities:
    1) The answers in the book are wrong.
    2) You have copied the problems incorrectly.
    3) You have accidently copied the answers for the wrong problem.
     
  4. Mar 5, 2013 #3
    Hmmm, this is strange. I knew my method was correct so I went on to the next set and still my answers are not matching the book! Thanks for your input :)
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted