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Angle question

  1. Mar 8, 2013 #1
    1. The problem statement, all variables and given/known data

    Estimate to the nearest degree, the angles that a diagonal of a box with dimensions 10cm x 15cm x 25cm makes with the edges of the box.


    2. Relevant equations

    [itex]cos\theta =\frac{u\cdot v}{\left \| u \right \|\left \| v \right \|}[/itex]


    3. The attempt at a solution

    For the angle between the diagonal vector and the edge with the 10cm side:

    [itex]u=(10,0,0)[/itex]
    [itex]v=(10,15,25)[/itex]

    [itex]cos\theta =\frac{(10,0,0)\cdot (10,15,25)}{\sqrt100\sqrt{100+225+625}}[/itex]
    [itex]cos\theta =\frac{100}{10\sqrt{950}}[/itex]

    [itex]cos\theta =\frac{10}{\sqrt{950}}[/itex]

    Theta = ~71 degrees?

    thanks, any help appreciated!
     
    Last edited: Mar 8, 2013
  2. jcsd
  3. Mar 8, 2013 #2
    Your denominator should be the product of the lengths of the two vectors. Vector u has length 10, right? Where's that? Vector v has length sqrt(950), why did you edit that to 100sqrt(850)?
     
  4. Mar 8, 2013 #3
    Oh yeah, I had it right the first time. But if I do that then I cant carry out the next step.. how would you proceed in this question?
     
  5. Mar 8, 2013 #4
    I edited it now, does it look right?
     
  6. Mar 8, 2013 #5
    Yeah, that looks right.
     
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