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What is this shape called?

  1. Jun 21, 2011 #1

    Femme_physics

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    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Jun 21, 2011 #2

    micromass

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    Hi FP! :smile:

    A pentagon is a good name for this. A pentagon is just a thingy with 5 corners and 5 sides.
    It isn't a regular pentagon though, for that we would require all sides and all angles to be equal.
     
  4. Jun 21, 2011 #3

    Pengwuino

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    Giant diamond.
     
  5. Jun 21, 2011 #4

    Femme_physics

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    Hi micromass! :) (I love this new "hi" thing lol!)

    The reason I'm asking is that I'm trying to find X here

    http://img10.imageshack.us/img10/3268/yjjjj.jpg [Broken]

    And I know the area is 3375 cm squared. I was hoping the relate the formula for area for this shape to X, but I'm unable to find its formula on my formula page (I can't find the shape, even)

    Oh, and there's no "diamond" there :P
     
    Last edited by a moderator: May 5, 2017
  6. Jun 21, 2011 #5

    micromass

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    Ah, I see. Well, I guess the area of a parallellogram is on your formula page?

    Well, let's try to find a formula for the giant diamond (I love that name :biggrin:)

    The trick is to subdivide the giant diamond into a parallellogram and a triangle. Just take the two mid-vertices (not the vertices on top and not the vertex on the bottom) and connect them with a line. Now the top is a parallellogram and the bottom is a triangle. Can you find the area of the parallellogram and the triangle?
     
  7. Jun 21, 2011 #6

    eumyang

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    I think you mean a trapezoid, not a parallelogram.
     
  8. Jun 21, 2011 #7

    micromass

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    Yes, indeed. Sorry for the confusion! :blushing:
     
  9. Jun 21, 2011 #8

    NascentOxygen

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    The figure is symmetrical about that dotted centre line, so concentrate on finding the area of just one of those halves and make it easier for yourself. :surprised

    Divide the shape up into simpler shapes whose area you can find, viz., rectangles and triangles. Looks like the height of the lowest triangle will be (X - 30). Add the areas together, and equate them to half of 3375 cm2

    You end up with one equation and one unknown. Solve for X. :smile:
     
  10. Jun 21, 2011 #9

    Femme_physics

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    Hmm.. I see what you're saying! That's brilliant.

    I can just take a trapezoid area and add the triangle's area, like that


    http://img695.imageshack.us/img695/5277/triy.jpg [Broken]

    Though from some reason I've still gotten the wrong X. Is this the right equation?
     
    Last edited by a moderator: May 5, 2017
  11. Jun 21, 2011 #10

    micromass

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    Yes, that seems to be the correct formula. Weird that you find the incorrect X now...
     
  12. Jun 21, 2011 #11
    My late Uncle Jor-el says it's our old family crest. He says it should have a big "S" in it.
     
  13. Jun 21, 2011 #12

    eumyang

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    That's a bit more work than Micromass' method, IMO.

    What did you get for X, and what was the answer supposed to be?
     
  14. Jun 21, 2011 #13

    Femme_physics

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    It's X = 75 which I actually got -- I forgot to multiply the other side by 2 *oops*

    Thanks, everyone!
     
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