Results 1 to 2 of 2

Math Help - URGENT! Find Angle between between vectors using norms

  1. #1
    Newbie
    Joined
    May 2012
    From
    North America
    Posts
    11

    Angry URGENT! Find Angle between between vectors using norms

    View image: PROB

    I don't understand how to use the information given. It's not like I can break up a sum inside a norm. I also don't know if this is in R^2 or R^3, so it's R^n

    I know the formula:

    cos theta = (u . v ) / ( ||u|| ||v|| )

    and that norm squared is a vector dot itself
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,661
    Thanks
    1616
    Awards
    1

    Re: URGENT! Find Angle between between vectors using norms

    Quote Originally Posted by LightRay7 View Post
    View image: PROB
    I know the formula:
    cos theta = (u . v ) / ( ||u|| ||v|| )
    and that norm squared is a vector dot itself

    All you need is th value of \vec{a}\cdot\vec{b}

    \begin{align*}100 &=\|\vec{a}+3\vec{b}\|^2\\ &= \vec{a}\cdot\vec{a}+9 \vec{b}\cdot\vec{b}+6\vec{a}\cdot\vec{b} \\ &=25+27+6 \vec{a}\cdot\vec{b}\\ 8&= \vec{a}\cdot \vec{b}  \end{align*}.
    Last edited by Plato; February 3rd 2013 at 08:31 AM.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Find angle in 3D space, from two vectors
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: June 19th 2010, 12:01 AM
  2. Find the angle between vectors r(t) and F(t)
    Posted in the Calculus Forum
    Replies: 4
    Last Post: July 28th 2008, 02:39 PM
  3. Replies: 4
    Last Post: April 9th 2008, 04:04 AM
  4. How can I find the angle between two vectors?
    Posted in the Pre-Calculus Forum
    Replies: 6
    Last Post: August 3rd 2007, 09:02 AM
  5. find angle between vectors .. confusion.
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: March 12th 2007, 05:05 AM

Search Tags


/mathhelpforum @mathhelpforum