1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Angle between two vectors

  1. Jun 9, 2014 #1
    Hi Guys,

    Im working on finding an angle between two vectors.

    a [ 1,2,3 ]
    b [ 4, -1, 0]

    //a// = sqrt(1^2+2^2+3^2) = sqrt14
    //b// = sqrt(4^2+(-1)^2+0^2 = sqrt17

    Dot product
    1.4 + 2.-1 + 3.0 = 2

    cos^-1 2/ sqrt14 sqrt17
    cos^-1 (1/( ???? )

  2. jcsd
  3. Jun 9, 2014 #2


    User Avatar
    Homework Helper

    What is the problem? The cosine of the angle is ##\frac{2}{\sqrt{17}\sqrt{14}}##. Just type in to your calculator, and take 'inverse cosine' of the result.

    And next time write out the parentheses. cos^-1 2/ sqrt14 sqrt17 means cos^-1(2) * sqrt(14) *sqrt(17) which has no sense.

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted