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Scalar product to find angle between two vectors

  1. Sep 16, 2007 #1
    Use the definition of scalar product, a·b = ab cos , and the fact that a·b = axbx + ayby + azbz (see Problem 46) to calculate the angle between the two vectors given by a = 2.0 i + 6.0 j + 2.0 k and b = 4.0 i + 3.0 j + 6.0 k.

    AdotB= 8i + 18j + 12k

    A=sqrt(2^2 + 6^2 + 2^2)=6.63
    B=sqrt(4^2 + 3^2 + 6^2)=7.81

    AdotB=(6.63)(7.81)cosΘ

    Θ=acos(38/51.78)

    Θ=42.79=WRONG
     
  2. jcsd
  3. Sep 16, 2007 #2
    Check your arithmetic.
     
  4. Sep 16, 2007 #3
    I went over it again and got the same answer.
     
  5. Sep 16, 2007 #4
    Then why do you think it's wrong?
     
  6. Sep 16, 2007 #5
    because the online assignment is giving me a big fat red X. lol
     
  7. Sep 16, 2007 #6
    Then I'll admit to making whatever mistake you've apparently made. :D
     
  8. Sep 16, 2007 #7
    Never mind. Got it. I switched the values of ay and by. Thanks.
     
  9. Sep 16, 2007 #8
    :d.. dah
     
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