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: Question involving vector & magnitude

  1. Mar 13, 2012 #1
    1. The problem statement, all variables and given/known data
    "If a vector magnitude 10 is combined with a second vector, the two vectors have a sum with a magnitude of 18 and have a difference with a magnitude of 2√10. Rounded to the nearest hundredth of a degree, what is the measure of the smallest angle between the two vectors?

    2. Relevant equations

    cosθ = (u dotproduct v) / (|u||v|)

    3. The attempt at a solution

    : |u| = 10
    : |u+v| = 18
    : |u-v| = 2√10

    Can you tell me if I'm doing this the right way? If I am, how should I solve this?
  2. jcsd
  3. Mar 14, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    Looks fine so far. Now square the last two equations and write the lefthand sides in terms of the dot product.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook