How to Use Random Cut Theorem and Simple Probability

Learn or recall from "Elements", Book II, Proposition 4, that "If a straight line be cut at random, the square on the whole is equal to the squares on the segments and twice the rectangle contained by the segments.", Learn or recall that, per the...

17 Steps 2 min read Advanced

Step-by-Step Guide

  1. Step 1: Learn or recall from "Elements"

    Grab/copy the yellow and orange diagram from this page onto the Clipboard.

    TYpe Command and c for copy to make a copy of the diagram.

    At the Desktop, click on the XL icon on the Dock to start Excel.

    Open a New Workbook in Excel.

    Holding down the Shift Key, do Edit Paste Picture into a new worksheet.

    Save the file under an appropriate filename into a logical folder, and make notes from the steps below, below the diagram.
  2. Step 2: Book II

    Stated another way, if x = y+z, then x^2 = (y+z)^2 = y^2 + 2yz + z^2.

    In the diagram then, square HF = y^2, square CK = z^2, rectangle AG = yz and rectangle GE = yz as well. ,,, where the next random event will be.

    There is a .3 * .7 = 21% chance the next event will be in one of the two rectangles, and so a 42% chance it will be in either rectangle (or in 2yz).

    There is a .3 *.3 = 9% chance the next event will be in square CK (or in z^2).

    There is a .7 * .7 = 49% chance the next event will be in square HF (or in y^2). (.42 + .09 + .49 =
    1.00 = 100% chance there will be a next event (presumably).

    This is an important assumption and not always the case.

    Or perhaps it's a presumption.

    It's in the sump somewhere, speaking etymologically ... , It's still very usable information today.

    A random cut of a card deck, a random cut in an accident, a random cut in Nature, etc., etc.
    -- all subject to analysis because of Euclid. , For more art charts and graphs, you might also want to click on Category:
    Microsoft Excel Imagery, Category:
    Mathematics, Category:
    Spreadsheets or Category:
    Graphics to view many Excel worksheets and charts where Trigonometry, Geometry and Calculus have been turned into Art, or simply click on the category as appears in the upper right white portion of this page, or at the bottom left of the page.
  3. Step 3: Proposition 4

  4. Step 4: that "If a straight line be cut at random

  5. Step 5: the square on the whole is equal to the squares on the segments and twice the rectangle contained by the segments."

  6. Step 6: Learn or recall that

  7. Step 7: per the above diagram

  8. Step 8: if segment AC = x and segment CB = y

  9. Step 9: that (x+y)^2 also equals x^2 + y^2 + 2xy.

  10. Step 10: Call the Area of the Whole square AE equal to 1 or 100% Probability.

  11. Step 11: Guesstimate from the random cut in the diagram that it occurred at a value of .70 of length AB.

  12. Step 12: Calculate from your guesstimate what a dart's chance's of landing in each square are

  13. Step 13: or where the next robbery will be

  14. Step 14: It's important to remember that Euclid solved this about 2.300 years ago!

  15. Step 15: Make use of helper articles when proceeding through this tutorial: See the article How to Describe a Square on a Given Line AB for a list of articles related to Euclid

  16. Step 16: Geometric and/or Trigonometric Art

  17. Step 17: Charting/Diagramming and Algebraic Formulation.

Detailed Guide

Grab/copy the yellow and orange diagram from this page onto the Clipboard.

TYpe Command and c for copy to make a copy of the diagram.

At the Desktop, click on the XL icon on the Dock to start Excel.

Open a New Workbook in Excel.

Holding down the Shift Key, do Edit Paste Picture into a new worksheet.

Save the file under an appropriate filename into a logical folder, and make notes from the steps below, below the diagram.

Stated another way, if x = y+z, then x^2 = (y+z)^2 = y^2 + 2yz + z^2.

In the diagram then, square HF = y^2, square CK = z^2, rectangle AG = yz and rectangle GE = yz as well. ,,, where the next random event will be.

There is a .3 * .7 = 21% chance the next event will be in one of the two rectangles, and so a 42% chance it will be in either rectangle (or in 2yz).

There is a .3 *.3 = 9% chance the next event will be in square CK (or in z^2).

There is a .7 * .7 = 49% chance the next event will be in square HF (or in y^2). (.42 + .09 + .49 =
1.00 = 100% chance there will be a next event (presumably).

This is an important assumption and not always the case.

Or perhaps it's a presumption.

It's in the sump somewhere, speaking etymologically ... , It's still very usable information today.

A random cut of a card deck, a random cut in an accident, a random cut in Nature, etc., etc.
-- all subject to analysis because of Euclid. , For more art charts and graphs, you might also want to click on Category:
Microsoft Excel Imagery, Category:
Mathematics, Category:
Spreadsheets or Category:
Graphics to view many Excel worksheets and charts where Trigonometry, Geometry and Calculus have been turned into Art, or simply click on the category as appears in the upper right white portion of this page, or at the bottom left of the page.

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