Math help.. Algebra and Geometry...

Discussion in 'After Hours Lounge (Off Topic)' started by Andrew S, Dec 13, 2003.

  1. Andrew S

    Andrew S Stunt Coordinator

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    I'm taking an Algebra and Geometry class through correspondance and I'm having some troubles with a couple questions...

    52. If vector a and vector b are unit vectors and the angle (theta) between them is 120 degrees, calculate
    (5a-b)*(a+b)

    The second question is pretty much the same setup...

    I know that I have to use the equation:
    cos theta = a * b / |a||b|

    I just get lost interpretting the significance of a and b being unit vectors?

    Any tips would be greatly appreciated

    Thanks,
    Andrew
     
  2. Garrett Lundy

    Garrett Lundy Producer

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    [​IMG] My head hurts. I go sleepy now.
     
  3. Andrew S

    Andrew S Stunt Coordinator

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    lol.. turns out unit vector means I just make it equal 1. duh...
     
  4. Dome Vongvises

    Dome Vongvises Lead Actor

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    Vectors, as you'll learn in physics, are quantities that possess both magnitude and direction.
     
  5. Andrew Testa

    Andrew Testa Second Unit

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    Andrew,

    You pretty much got it. a unit vector is a vector with a length (magnitude) of 1, regardless of its direction. So if the question was asking you to use the vector length in the calculation, just use 1, and the angle was a red herring.

    Andy
     
  6. george kaplan

    george kaplan Executive Producer

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    Well something's funky.

    If cos theta = a * b / |a||b|

    then cos(theta)=1*1/1*1=1

    but cos(120)=.8142

    so it would appear that the a & b don't represent length of the vector, since it's certainly possible to have two unit vectors with an angle of 120 degrees. I don't know what a & b are supposed to be in that formula for the cos (theta), but it isn't length.
     
  7. Holadem

    Holadem Lead Actor

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  8. Will Pomeroy

    Will Pomeroy Stunt Coordinator

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  9. Joseph Howard

    Joseph Howard Stunt Coordinator

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    Careful about helping. There are many final exams
    occuring right now. Both in traditional classes and
    via correspondance courses.

    Hate to cause a problem, but be careful.

    Dr. Joe
     

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