Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Addition of Vectors

  1. May 21, 2012 #1
    To add two vectors, a[itex]\rightarrow[/itex] and b[itex]\rightarrow[/itex] we use the formula [itex]\sqrt{}[/itex]a2+b2+2abcosθ

    where θ is the smallest angle between vectors a and b. Is there any way I can use the bigger angle to calculate the sum ? It's not a homework, just a question from my intution.

    I have attached a pic also... Thanks in advance for help

    Attached Files:

  2. jcsd
  3. May 21, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper

    hi physics kiddy! :smile:
    you mean 360° - θ ?

    but cos(360° - θ) equals cosθ :confused:

    btw, the formula is easier to understand if you draw a and b head-to-tail (instead of tail-to-tail) :wink:
  4. May 21, 2012 #3
    To use the bigger angle, all you need to do is to express cos(360-x) in terms of cos(x), which in fact is cos(360-x) = cos(x) :wink:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook