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Homework Help: Length of diagonal from bottom to top

  1. Jul 29, 2017 #1
    length of botton to top diagonal of a solid p462.jpg 1. The problem statement, all variables and given/known data

    I have to find the length of a diagonal from bottom to top. I dont know which formula i would be using? Please see the attachment for more information.
    2. Relevant equations

    May be pythagorous theorem. But i dont know which sides i have to select
    3. The attempt at a solution
    Sorry i need some hint.
  2. jcsd
  3. Jul 29, 2017 #2


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    Add one more line to the sketch and the way to solve this problem should become easier for you to see . The added line goes from point A to the point vertically below point B .
    Last edited: Jul 29, 2017
  4. Jul 29, 2017 #3


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    To add to @Nidum 's comment:

    The added line goes from point A to the corner of the box vertically below point B .
  5. Jul 29, 2017 #4


    Staff: Mentor

    You'll need to use Pythagoras theorem twice.
  6. Aug 1, 2017 #5
    Try thinking of the line drawn as the vector <10, 7, 2>
  7. Aug 2, 2017 #6
    Thanks everybody. Post# 3 provided a clue but i came to know about this when i solved the problem. The other clue is the application of pythagorus theorem on rectangular solids which i got from the following link: https://www.google.com.pk/imgres?im...ved=0ahUKEwiA__Hz3LjVAhVHBcAKHQACAMEQ9QEIJzAA

    Let K be the point below B & C is connected to both A & K
    AK^2 = AC^2 + CK^2
    AB^2 = AK^2 + BK^2
    AB^2 = AC^2 + CK^2 + BK^2 = 100 + 49 + 4 therefore AB = 3sqrt(17).


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