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Homework Help: Geometry Equation Problem

  1. Feb 26, 2006 #1
    in the textbook it says cos^2x + cos^2y + cos^2z=1 . How do we do cos^2?
  2. jcsd
  3. Feb 26, 2006 #2
    What do you mean "How do we do cos^2" ? I don't understand the question that you're asking, could you elaborate a little bit?
  4. Feb 26, 2006 #3
    hmm....like, how do they get =1? What would I type into hte calculator to get that? The textbook wasn't very helpful in that sense.
  5. Feb 26, 2006 #4

    Well it certainly isn't an identity. What is this in the context of, I mean how is this presented in the book? Is it a problem or what?
  6. Feb 26, 2006 #5
    That's all it says. I'll ask the teacher tomorrow to elaborate and get back to you.
  7. Feb 26, 2006 #6
    But is this a problem, or just something like in an example or diagram? I'm sorry I couldn't be more help, it's just it's a very vague statement that I'm having a hard time inferring things from.
  8. Feb 26, 2006 #7
    It's the equation that is given.
  9. Feb 26, 2006 #8
    And it says nothing else, no conditions or what the equation is supposed to be or be used for? I just have a hard time believing that something like this would be put in a textbook without any explanation if you are supposed to be learning it.
  10. Feb 26, 2006 #9
    Could x, y, and z be Euler angles? That's the only relationship I know of that looks like that.

  11. Feb 27, 2006 #10


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    That's was my first thought: L is a line in 3 dimensions and x, y, z are the "Euler angles", the angles L makes with the x, y, z axes respectively. In that case, it must be the case that cos2 x+ cos2 y+ cos2 z= 1. In fact, (cos x)i+ (cos y)j+ (cos z)k is a unit vector pointing in the direction of line L.

    But Hollysmoke's question was how to enter the numbers into the calculator!

    Hollysmoke, we really can't answer that without knowing what kind of calculator you are using. Different types of calculator require different kinds of entry. Also what are your values for x, y, z?
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