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eroshea

  • 3 years ago

An isosceles triangle ABC, in which AB=BC=6 root 2 and AC=12 is folded along the altitude BD so that planes ABD and BDC form a right dihedral angle. Find the angle between side AB and its new position.

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  1. experimentX
    • 3 years ago
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    could you draw a bit of figure?

  2. eroshea
    • 3 years ago
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    i can't .. that is my problem, too..

  3. experimentX
    • 3 years ago
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    |dw:1353425869624:dw|

  4. experimentX
    • 3 years ago
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    |dw:1353426012864:dw|

  5. eroshea
    • 3 years ago
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    so what i'm going to find is the theta??

  6. eroshea
    • 3 years ago
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    Find the angle between side AB and its new position. what does this mean?

  7. experimentX
    • 3 years ago
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    i guess that's the angle you are going to find ... can you find it?

  8. eroshea
    • 3 years ago
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    i need further solution/explanation

  9. experimentX
    • 3 years ago
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    |dw:1353426445410:dw|

  10. eroshea
    • 3 years ago
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    that is 90 degrees

  11. eroshea
    • 3 years ago
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    i used cosine law

  12. experimentX
    • 3 years ago
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    \( \theta \) will be half of \( \alpha \)

  13. eroshea
    • 3 years ago
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    45 ?

  14. eroshea
    • 3 years ago
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    the book's answer is 60 degrees.. but i find it 45 degrees.. how did it ended up with 60?

  15. experimentX
    • 3 years ago
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    yep .. should be around like that if you did it properly!!

  16. eroshea
    • 3 years ago
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    aawww. can you explain it ?

  17. experimentX
    • 3 years ago
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    looks like you did it right http://www.wolframalpha.com/input/?i=12^2+%3D+2%286+sqrt%282%29%29^2+-+2+*+%286+sqrt%282%29%29^2+cos%28x%29

  18. eroshea
    • 3 years ago
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    b^2 = a^2 + c^2 - 2ac cos theta that is cosine law right? and the answer is 90 degrees

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